Hypothermic and cryogenic preservation of cardiac tissue-engineered constructs.

Cardiac tissue engineering (cTE) has already advanced towards the first clinical trials, investigating safety and feasibility of cTE construct transplantation in failing hearts. However, the lack of well-established preservation methods poses a hindrance to further scalability, commercialization, and transportation, thereby reducing their clinical implementation. In this study, hypothermic preservation (4 °C) and two methods for cryopreservation (i.e., a slow and fast cooling approach to -196 °C and -150 °C, respectively) were investigated as potential solutions to extend the cTE construct implantation window. The cTE model used consisted of human induced pluripotent stem cell-derived cardiomyocytes and human cardiac fibroblasts embedded in a natural-derived hydrogel and supported by a polymeric melt electrowritten hexagonal scaffold. Constructs, composed of cardiomyocytes of different maturity, were preserved for three days, using several commercially available preservation protocols and solutions. Cardiomyocyte viability, function (beat rate and calcium handling), and metabolic activity were investigated after rewarming. Our observations show that cardiomyocytes' age did not influence post-rewarming viability, however, it influenced construct function. Hypothermic preservation with HypoThermosol® ensured cardiomyocyte viability and function. Furthermore, fast freezing outperformed slow freezing, but both viability and function were severely reduced after rewarming. In conclusion, whereas long-term preservation remains a challenge, hypothermic preservation with HypoThermosol® represents a promising solution for cTE construct short-term preservation and potential transportation, aiding in off-the-shelf availability, ultimately increasing their clinical applicability.

Impaired Response to Mismatch Novelty in the Li2+-Pilocarpine Rat Model of TLE: Correlation with Hippocampal Monoaminergic Inputs.

Novelty detection, crucial to episodic memory formation, is impaired in epileptic patients with mesial temporal lobe resection. Mismatch novelty detection, that activates the hippocampal CA1 area in humans and is vital for memory reformulation and reconsolidation, is also impaired in patients with hippocampal lesions. In this work, we investigated the response to mismatch novelty, as occurs with the new location of known objects in a familiar environment, in the Li2+-pilocarpine rat model of TLE and its correlation with hippocampal monoaminergic markers. Animals showing spontaneous recurrent seizures (SRSs) for at least 4 weeks at the time of behavioural testing showed impaired spatial learning in the radial arm maze, as described. Concurrently, SRS rats displayed impaired exploratory responses to mismatch novelty, yet novel object recognition was not significantly affected in SRS rats. While the levels of serotonin and dopamine transporters were mildly decreased in hippocampal membranes from SRS rats, the levels on the norepinephrine transporter, tyrosine hydroxylase and dopamine-ß-hydroxylase were enhanced, hinting for an augmentation, rather than an impairment in noradrenergic function in SRS animals. Altogether, this reveals that mismatch novelty detection is particularly affected by hippocampal damage associated to the Li2+-pilocarpine model of epilepsy 4-8 weeks after the onset of SRSs and suggests that deficits in mismatch novelty detection may substantially contribute to cognitive impairment in MTLE. As such, behavioural tasks based on these aspects of mismatch novelty may prove useful in the development of cognitive therapy strategies aiming to rescue cognitive deficits observed in epilepsy.

GET-UP Trial 1-year results: long-term impact of an early mobilization protocol on functional performance after surgery for chronic subdural hematoma.

OBJECTIVE: Evidence on timing for mobilization after chronic subdural hematoma (cSDH) surgery is heterogeneous, and practices differ considerably among neurosurgical centers. The Impact of an Early Out-of-Bed Paradigm in Postoperative Outcomes of Chronic Subdural Hematomas: GET-UP Randomized Prospective Trial (GET-UP Trial) is a randomized clinical trial comparing a postoperative early mobilization protocol to bed rest. Previously reported results at clinical discharge and 1 month after surgery indicated a decreased risk of medical complications in the early mobilization group. Herein, the authors report outcomes at the 1-year follow-up. METHODS: The GET-UP Trial is a prospective, randomized, unicentric, open-label study with an intention-to-treat primary analysis designed to evaluate the impact of an early mobilization protocol after burr hole craniostomy for cSDH on the occurrence of medical complications and functional outcomes. Between January 2019 and August 2021, a total of 208 patients were recruited and randomized to either an early mobilization group, in which patients began elevation of the head of the bed within the first 12 hours after surgery, or to a bed rest group, in which patients remained recumbent for 48 hours. Outcomes assessed at the 1-year follow-up included functional status as measured by the Glasgow Outcome Scale-Extended (GOSE) and repeat surgery for hematoma recurrence (surgical recurrence). RESULTS: A total of 203 patients completed 1 year of follow-up: 101 in the bed rest group and 102 in the early mobilization group. No significant baseline pre-randomization clinical differences were observed between the two management groups. At 1 year after surgery, a favorable functional outcome, defined as a GOSE score ≥ 5, was observed in 59 patients (58.4%) in the bed rest group and 78 (76.5%) in the early mobilization group (p = 0.006). Death occurred in 25 patients (24.8%) in the bed rest group and 16 (15.7%) in the early mobilization group (p = 0.108). Surgical recurrence was noted in 6 patients (5.9%) in the bed rest group and 7 (6.9%) in the early mobilization group (p = 0.788). Multivariate analysis showed an independent association between early mobilization and an increase in favorable functional outcomes (OR 2.006, 95% CI 1.076-3.739, p = 0.028). CONCLUSIONS: The GET-UP Trial is the first randomized clinical trial assessing the impact of mobilization strategies on medical complications after burr hole craniostomy for cSDH. Regarding functional results 1 year after surgery, early mobilization was associated with an improvement in functional outcomes without an increase in surgical recurrence. These findings support the preference for an early mobilization protocol in cSDH patients over mandatory bed rest strategies.

Corrigendum: Consistent long-term therapeutic efficacy of human umbilical cord matrix-derived mesenchymal stromal cells after myocardial infarction despite individual differences and transient engraftment.

[This corrects the article DOI: 10.3389/fcell.2021.624601.].

Chitosan 3D scaffolds with resolvin D1 for vertebral arthrodesis: a pilot study.

PURPOSE: Over the last years, the number of vertebral arthrodesis has been steadily increasing. The use of iliac crest bone autograft remains the "gold standard" for bone graft substitute in these procedures. However, this solution has some side effects, such as the problem of donor site morbidity indicating that there is a real need for adequate alternatives. This pilot study aimed to evaluate the usefulness of chitosan (Ch) porous 3D scaffolds incorporated with resolvin D1 (RvD1) as an alternative implant to iliac bone autograft. METHODS: We have performed bilateral posterolateral lumbar vertebral arthrodesis in a rat animal model. Three experimental groups were used: (i) non-operated animals; (ii) animals implanted with Ch scaffolds incorporated with RvD1 and (iii) animals implanted with iliac bone autograft. RESULTS: The collagenous fibrous capsule formed around the Ch scaffolds with RvD1 is less dense when compared with the iliac bone autograft, suggesting an important anti-inflammatory effect of RvD1. Additionally, new bone formation was observed in the Ch scaffolds with RvD1. CONCLUSION: These results demonstrate the potential of these scaffolds for bone tissue repair applications.

Impact of an early mobilization protocol on the reduction of medical complications after surgery for chronic subdural hematoma: the GET-UP Trial.

OBJECTIVE: Timing of mobilization after chronic subdural hematoma (cSDH) surgery is highly heterogeneous among neurosurgical centers. Past studies have suggested that early mobilization may reduce medical complications without increasing recurrence, but evidence remains scarce. The purpose of this study was to compare an early mobilization protocol with a 48-hour bed rest practice, with a focus on the occurrence of medical complications. METHODS: The GET-UP Trial is a prospective, randomized, unicentric, open-label study with an intention-to-treat primary analysis designed to evaluate the impact of an early mobilization protocol after burr hole craniostomy for cSDH on the occurrence of medical complications and functional outcomes. A total of 208 patients were recruited and randomly assigned to either an early mobilization group where they began head-of-bed elevation within the first 12 hours after surgery and proceeded to sedestation, orthostatism, and/or walking as rapidly as tolerated, or to a bed rest group where they remained recumbent with a head-of-bed angle inferior to 30° for 48 hours after surgery. The primary outcome was the occurrence of a medical complication (defined as either an infection, seizure, or thrombotic event) after surgery and until clinical discharge. Secondary outcomes included length of stay measured from randomization to clinical discharge, surgical hematoma recurrence at clinical discharge and 1 month after surgery, and Glasgow Outcome Scale-Extended (GOSE) assessment at clinical discharge and 1 month after surgery. RESULTS: A total of 104 patients were randomly assigned to each group. No significant baseline clinical differences were observed before randomization. The primary outcome occurred in 36 (34.6%) patients included in the bed rest group and 20 (19.2%) in the early mobilization group (p = 0.012). At 1 month after surgery, a favorable functional outcome (defined as GOSE score ≥ 5) was observed in 75 (72.1%) patients in the bed rest group and 85 (81.7%) in the early mobilization group (p = 0.100). Surgical recurrence occurred in 5 (4.8%) patients in the bed rest group and 8 (7.7%) in the early mobilization group (p = 0.390). CONCLUSIONS: The GET-UP Trial is the first randomized clinical trial to assess the impact of mobilization strategies on medical complications after burr hole craniostomy for cSDH. Early mobilization was associated with a reduction in medical complications without a significant effect on surgical recurrence, compared with a 48-hour bed rest protocol.

Generation, High-Throughput Screening, and Biobanking of Human-Induced Pluripotent Stem Cell-Derived Cardiac Spheroids.

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are of paramount importance for human cardiac disease modeling and therapeutics. We recently published a cost-effective strategy for the massive expansion of hiPSC-CMs in two dimensions (2D). Two major limitations are cell immaturity and a lack of three-dimensional (3D) arrangement and scalability in high-throughput screening (HTS) platforms. To overcome these limitations, the expanded cardiomyocytes form an ideal cell source for the generation of 3D cardiac cell culture and tissue engineering techniques. The latter holds great potential in the cardiovascular field, providing more advanced and physiologically relevant HTS. Here, we describe an HTS-compatible workflow with easy scalability for the generation, maintenance, and optical analysis of cardiac spheroids (CSs) in a 96-well-format. These small CSs are essential to fill the gap present in current in vitro disease models and/or generation for 3D tissue engineering platforms. The CSs present a highly structured morphology, size, and cellular composition. Furthermore, hiPSC-CMs cultured as CSs display increased maturation and several functional features of the human heart, such as spontaneous calcium handling and contractile activity. By automatization of the complete workflow, from the generation of CSs to functional analysis, we increase intra- and inter-batch reproducibility as demonstrated by high-throughput (HT) imaging and calcium handling analysis. The described protocol allows modeling of cardiac diseases and assessing drug/therapeutic effects at the single-cell level within a complex 3D cell environment in a fully automated HTS workflow. In addition, the study describes a straightforward procedure for long-term preservation and biobanking of whole-spheroids, thereby providing researchers the opportunity to create next-generation functional tissue storage. HTS combined with long-term storage will substantially contribute to translational research in a wide range of areas, including drug discovery and testing, regenerative medicine, and the development of personalized therapies.

Circadian Dependence of the Acute Immune Response to Myocardial Infarction.

Circadian rhythms influence the recruitment of immune cells and the onset of inflammation, which is pivotal in the response to ischemic cardiac injury after a myocardial infarction (MI). The hyperacute immune response that occurs within the first few hours after a MI has not yet been elucidated. Therefore, we characterized the immune response and myocardial damage 3 hours after a MI occurs over a full twenty-four-hour period to investigate the role of the circadian rhythms in this response. MI was induced at Zeitgeber Time (ZT) 2, 8, 14, and 20 by permanent ligation of the left anterior descending coronary artery. Three hours after surgery, animals were terminated and blood and hearts collected to assess the immunological status and cardiac damage. Blood leukocyte numbers varied throughout the day, peaking during the rest-phase (ZT2 and 8). Extravasation of leukocytes was more pronounced during the active-phase (ZT14 and 20) and was associated with greater chemokine release to the blood and expression of adhesion molecules in the heart. Damage to the heart, measured by Troponin-I plasma levels, was elevated during this time frame. Clock gene oscillations remained intact in both MI-induced and sham-operated mice hearts, which could explain the circadian influence of the hyperacute inflammatory response after a MI. These findings are in line with the clinical observation that patients who experience a MI early in the morning (i.e., early active phase) have worse clinical outcomes. This study provides further insight on the immune response occurring shortly after an MI, which may contribute to the development of novel and optimization of current therapeutic approaches.

Long term outcome of functional hemispherectomy for refractory epilepsy: Experience from a single center.

BACKGROUND: Hemispherectomy has an established role as a treatment of last resort in patients with unilateral hemispheric lesions suffering from refractory epilepsy. METHODS: Seven patients were evaluated at our Epilepsy Unit. We compared the seizure outcome at 6 months, 1, 2, 5 years post-surgery, as well as at end follow-up (mean 7.1 years) using Engel classification. Reduction of antiepileptic drugs (AEDs) was also assessed utilizing equal time frames. RESULTS: The mean age of seizure onset was 5.4 years. Engel I was achieved in 5 patients at 6 months (71.4%). Engel at 1 year was predicted by the Engel at 6 months (p=0.013) with a similar number of patients being classified as Engel I outcome. Engel at 2 years was also predicted by Engel at 6 months and at 1 year (p=0.030). At end follow-up only 3 patients (42.9%) remained categorized as Engel I outcome. There was a trend toward a stability in Engel classification. All patients with developmental causes for their epilepsy experienced some deterioration of the surgical outcomes. Conversely, all patients with acquired causes were stable throughout follow-up. Seizure outcome at 6 months was worse in the patients who had post-op complications (p=0.044). Adult and pediatric populations did not differ significantly in any tested variable. CONCLUSIONS: Hemispherectomy is a valuable resource for seizure control in properly selected patients. Engel patient's evolution could be predicted at 6 months interval. Hemispherectomy could be considered a useful attitude in difficult cases.

Intercellular transfer of miR-200c-3p impairs the angiogenic capacity of cardiac endothelial cells.

As mediators of intercellular communication, extracellular vesicles containing molecular cargo, such as microRNAs, are secreted by cells and taken up by recipient cells to influence their cellular phenotype and function. Here we report that cardiac stress-induced differential microRNA content, with miR-200c-3p being one of the most enriched, in cardiomyocyte-derived extracellular vesicles mediates functional cross-talk with endothelial cells. Silencing of miR-200c-3p in mice subjected to chronic increased cardiac pressure overload resulted in attenuated hypertrophy, smaller fibrotic areas, higher capillary density, and preserved cardiac ejection fraction. We were able to maximally rescue microvascular and cardiac function with very low doses of antagomir, which specifically silences miR-200c-3p expression in non-myocyte cells. Our results reveal vesicle transfer of miR-200c-3p from cardiomyocytes to cardiac endothelial cells, underlining the importance of cardiac intercellular communication in the pathophysiology of heart failure.

HIPTCN: Prospective Observational Study of Hypocoagulated Head Trauma Patients with Normal Admission Computed Tomography Scan.

INTRODUCTION: Our national protocol for traumatic brain injury dictates that hypocoagulated patients with mild trauma and initial tomography scan with no intracranial traumatic changes must be hospitalized for 24 hours and do a post-surveillance tomography scan. The main goal of this study was to evaluate the clinical relevance of these measures. MATERIAL AND METHODS: A prospective observational study was undertaken in four hospitals. Adult hypocoagulated traumatic brain injury patients with a normal tomography scan were included. The main outcomes evaluated were rate of delayed intracranial hemorrhage, rate of admission in a neurosurgical department, rate of complications related with surveillance and rate of prolonged hospitalization due to complications. An analysis combining data from a previously published report was also done. RESULTS: A total of 178 patients were included. Four patients (2.3%) had a delayed hemorrhage and three (1.7%) were hospitalized in a neurosurgery ward. No cases of symptomatic hemorrhage were identified. No surgery was needed, and all patients had their anticoagulation stopped. Complications during surveillance were reported in seven patients (3.9%), of which two required prolonged hospitalization. DISCUSSION: The rate of complications related with surveillance was higher than the rate of delayed hemorrhages. The initial period of in-hospital surveillance did not convey any advantage since the management of patients was never dictated by neurological changes. Post-surveillance tomography played a role in deciding about anticoagulation suspension and prolongation of hospitalization. CONCLUSION: Delayed hemorrhage is a rare event and the need for surgery even rarer. The need for in-hospital surveillance should be reassessed.

Introdução: O nosso protocolo nacional para traumatismos cranioencefálicos recomenda que doentes hipocoagulados com trauma craniano ligeiro e tomografia inicial sem alterações traumáticas intracranianas sejam hospitalizados 24 horas e façam uma tomografia computorizada pós-vigilância. O principal objetivo deste estudo foi avaliar a relevância clínica dessas medidas. Material e Métodos: Foi realizado em quatro hospitais um estudo prospetivo e observacional. Foram incluídos adultos hipocoagulados com trauma craniano e tomografia normal. Os principais outcomes avaliados foram: taxa de hemorragia intracraniana tardia, taxa de internamento numa enfermaria de neurocirurgia, taxa de complicações relacionadas com a vigilância e taxa de hospitalização prolongada por complicações. Resultados: Foram incluídos um total de 178 doentes. Quatro doentes (2,3%) apresentaram hemorragia tardia e três (1,7%) foram mantidos hospitalizados numa enfermaria de Neurocirurgia. Não foram documentados casos de hemorragia tardia sintomática. Nenhuma cirurgia foi necessária e em todos estes doentes a anticoagulação foi interrompida. Durante a vigilância, foram relatadas complicações em sete doentes (3,9%), dos quais dois exigiram hospitalização prolongada. Discussão: A taxa de complicações relacionadas com a vigilância foi maior do que a taxa de hemorragia tardia. O período inicial de vigilância intra-hospitalar não trouxe qualquer vantagem, já que o manejo dos doentes nunca foi ditado por alterações neurológicas. A tomografia pós-vigilância desempenhou um papel importante na decisão sobre a suspensão da anticoagulação e o prolongamento da hospitalização. Conclusão: A hemorragia tardia é um evento raro e a necessidade de cirurgia ainda mais. Deve ser reavaliada a necessidade de vigilância intra-hospitalar.

A microRNA program regulates the balance between cardiomyocyte hyperplasia and hypertrophy and stimulates cardiac regeneration.

Myocardial regeneration is restricted to early postnatal life, when mammalian cardiomyocytes still retain the ability to proliferate. The molecular cues that induce cell cycle arrest of neonatal cardiomyocytes towards terminally differentiated adult heart muscle cells remain obscure. Here we report that the miR-106b~25 cluster is higher expressed in the early postnatal myocardium and decreases in expression towards adulthood, especially under conditions of overload, and orchestrates the transition of cardiomyocyte hyperplasia towards cell cycle arrest and hypertrophy by virtue of its targetome. In line, gene delivery of miR-106b~25 to the mouse heart provokes cardiomyocyte proliferation by targeting a network of negative cell cycle regulators including E2f5, Cdkn1c, Ccne1 and Wee1. Conversely, gene-targeted miR-106b~25 null mice display spontaneous hypertrophic remodeling and exaggerated remodeling to overload by derepression of the prohypertrophic transcription factors Hand2 and Mef2d. Taking advantage of the regulatory function of miR-106b~25 on cardiomyocyte hyperplasia and hypertrophy, viral gene delivery of miR-106b~25 provokes nearly complete regeneration of the adult myocardium after ischemic injury. Our data demonstrate that exploitation of conserved molecular programs can enhance the regenerative capacity of the injured heart.

A Roadmap to Cardiac Tissue-Engineered Construct Preservation: Insights from Cells, Tissues, and Organs.

Worldwide, over 26 million patients suffer from heart failure (HF). One strategy aspiring to prevent or even to reverse HF is based on the transplantation of cardiac tissue-engineered (cTE) constructs. These patient-specific constructs aim to closely resemble the native myocardium and, upon implantation on the diseased tissue, support and restore cardiac function, thereby preventing the development of HF. However, cTE constructs off-the-shelf availability in the clinical arena critically depends on the development of efficient preservation methodologies. Short- and long-term preservation of cTE constructs would enable transportation and direct availability. Herein, currently available methods, from normothermic- to hypothermic- to cryopreservation, for the preservation of cardiomyocytes, whole-heart, and regenerative materials are reviewed. A theoretical foundation and recommendations for future research on developing cTE construct specific preservation methods are provided. Current research suggests that vitrification can be a promising procedure to ensure long-term cryopreservation of cTE constructs, despite the need of high doses of cytotoxic cryoprotective agents. Instead, short-term cTE construct preservation can be achieved at normothermic or hypothermic temperatures by administration of protective additives. With further tuning of these promising methods, it is anticipated that cTE construct therapy can be brought one step closer to the patient.

Long term outcome of functional hemispherectomy for refractory epilepsy: Experience from a single center.

BACKGROUND: Hemispherectomy has an established role as a treatment of last resort in patients with unilateral hemispheric lesions suffering from refractory epilepsy. METHODS: Seven patients were evaluated at our Epilepsy Unit. We compared the seizure outcome at 6 months, 1, 2, 5 years post-surgery, as well as at end follow-up (mean 7.1 years) using Engel classification. Reduction of antiepileptic drugs (AEDs) was also assessed utilizing equal time frames. RESULTS: The mean age of seizure onset was 5.4 years. Engel I was achieved in 5 patients at 6 months (71.4%). Engel at 1 year was predicted by the Engel at 6 months (p=0.013) with a similar number of patients being classified as Engel I outcome. Engel at 2 years was also predicted by Engel at 6 months and at 1 year (p=0.030). At end follow-up only 3 patients (42.9%) remained categorized as Engel I outcome. There was a trend toward a stability in Engel classification. All patients with developmental causes for their epilepsy experienced some deterioration of the surgical outcomes. Conversely, all patients with acquired causes were stable throughout follow-up. Seizure outcome at 6 months was worse in the patients who had post-op complications (p=0.044). Adult and pediatric populations did not differ significantly in any tested variable. CONCLUSIONS: Hemispherectomy is a valuable resource for seizure control in properly selected patients. Engel patient's evolution could be predicted at 6 months interval. Hemispherectomy could be considered a useful attitude in difficult cases.

From the freezer to the clinic: Antifreeze proteins in the preservation of cells, tissues, and organs.

Understanding the mechanisms by which natural anti-freeze proteins protect cells and tissues from cold could help to improve the availability of donor organs for transplantation.

Consistent Long-Term Therapeutic Efficacy of Human Umbilical Cord Matrix-Derived Mesenchymal Stromal Cells After Myocardial Infarction Despite Individual Differences and Transient Engraftment.

Human mesenchymal stem cells gather special interest as a universal and feasible add-on therapy for myocardial infarction (MI). In particular, human umbilical cord matrix-derived mesenchymal stromal cells (UCM-MSC) are advantageous since can be easily obtained and display high expansion potential. Using isolation protocols compliant with cell therapy, we previously showed UCM-MSC preserved cardiac function and attenuated remodeling 2 weeks after MI. In this study, UCM-MSC from two umbilical cords, UC-A and UC-B, were transplanted in a murine MI model to investigate consistency and durability of the therapeutic benefits. Both cellular products improved cardiac function and limited adverse cardiac remodeling 12 weeks post-ischemic injury, supporting sustained and long-term beneficial therapeutic effect. Donor associated variability was found in the modulation of cardiac remodeling and activation of the Akt-mTOR-GSK3ß survival pathway. In vitro, the two cell products displayed similar ability to induce the formation of vessel-like structures and comparable transcriptome in normoxia and hypoxia, apart from UCM-MSCs proliferation and expression differences in a small subset of genes associated with MHC Class I. These findings support that UCM-MSC are strong candidates to assist the treatment of MI whilst calling for the discussion on methodologies to characterize and select best performing UCM-MSC before clinical application.

Bone marrow contribution to the heart from development to adulthood.

Cardiac chamber walls contain large numbers of non-contractile interstitial cells, including fibroblasts, endothelial cells, pericytes and significant populations of blood lineage-derived cells. Blood cells first colonize heart tissues a few days before birth, although their recruitment from the bloodstream to the cardiac interstitium is continuous and extends throughout adult life. The bone marrow, as the major hematopoietic site of adult individuals, is in charge of renewing all circulating cell types, and it therefore plays a pivotal role in the incorporation of blood cells to the heart. Bone marrow-derived cells are instrumental to tissue homeostasis in the steady-state heart, and are major effectors in cardiac disease progression. This review will provide a comprehensive approach to bone marrow-derived blood cell functions in the heart, and discuss aspects related to hot topics in the cardiovascular field like cell-based heart regeneration strategies.

Stereological estimation of cardiomyocyte number and proliferation.

Cardiovascular diseases remain the leading cause of death, largely due to the limited regenerative capacity of the adult mammalian heart. Yet, neonatal mammals were shown to regenerate the myocardium after injury by increasing the proliferation of pre-existing cardiomyocytes. Re-activation of cardiomyocyte proliferation in adulthood has been considered a promising strategy to improve cardiac response to injury. Notwithstanding, quantification of cardiomyocyte proliferation, which occurs at a very low rate, is hampered by inefficient or unreliable techniques. Herein, we propose an optimized protocol to unequivocally assess cardiomyocyte proliferation and/or cardiomyocyte number in the myocardium. Resorting to a stereological approach we estimate the number of cardiomyocytes using representative thick sections of left ventricle fragments. This protocol overcomes the need for spatial-temporal capture of cardiomyocyte proliferation events by focusing instead on the quantification of the outcome of this process. In addition, assessment of cardiomyocyte nucleation avoids overestimation of cardiomyocyte proliferation due to increased binucleation. By applying this protocol, we were able to previously show that apical resection triggers proliferation of pre-existing cardiomyocytes generating hearts with more cardiomyocytes. Likewise, the protocol will be useful for any study aiming at evaluating the impact of neomyogenic therapies.