Persistent SARS-CoV-2 infection in patients seemingly recovered from COVID-19.

SARS-CoV-2 infection is clinically heterogeneous, ranging from asymptomatic to deadly. A few patients with COVID-19 appear to recover from acute viral infection but nevertheless progress in their disease and eventually die, despite persistent negativity at molecular tests for SARS-CoV-2 RNA. Here, we performed post-mortem analyses in 27 consecutive patients who had apparently recovered from COVID-19 but had progressively worsened in their clinical conditions despite repeated viral negativity in nasopharyngeal swabs or bronchioalveolar lavage for 11-300 consecutive days (average: 105.5 days). Three of these patients remained PCR-negative for over 9 months. Post-mortem analysis revealed evidence of diffuse or focal interstitial pneumonia in 23/27 (81%) patients, accompanied by extensive fibrotic substitution in 13 cases (47%). Despite apparent virological remission, lung pathology was similar to that observed in acute COVID-19 individuals, including micro- and macro-vascular thrombosis (67% of cases), vasculitis (24%), squamous metaplasia of the respiratory epithelium (30%), frequent cytological abnormalities and syncytia (67%), and the presence of dysmorphic features in the bronchial cartilage (44%). Consistent with molecular test negativity, SARS-CoV-2 antigens were not detected in the respiratory epithelium. In contrast, antibodies against both spike and nucleocapsid revealed the frequent (70%) infection of bronchial cartilage chondrocytes and para-bronchial gland epithelial cells. In a few patients (19%), we also detected positivity in vascular pericytes and endothelial cells. Quantitative RT-PCR amplification in tissue lysates confirmed the presence of viral RNA. Together, these findings indicate that SARS-CoV-2 infection can persist significantly longer than suggested by standard PCR-negative tests, with specific infection of specific cell types in the lung. Whether these persistently infected cells also play a pathogenic role in long COVID remains to be addressed. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Hidden left ventricular sarcoma manifesting itself with cardiogenic shock.

Cardiac sarcomas are rare and aggressive tumors that could have a multiorgan involvement and unfavorable prognosis. We present an extremely rare situation of cardiac sarcoma in a fragile elderly patient with a dramatic presentation of cardiogenic shock.

SARS-CoV-2, myocardial injury and inflammation: insights from a large clinical and autopsy study.

OBJECTIVE: Despite growing evidence about myocardial injury in hospitalized COronaVIrus Disease 2019 (COVID-19) patients, the mechanism behind this injury is only poorly understood and little is known about its association with SARS-CoV-2-mediated myocarditis. Furthermore, definite evidence of the presence and role of SARS-CoV-2 in cardiomyocytes in the clinical scenario is still lacking. METHODS: We histologically characterized myocardial tissue of 40 patients deceased with severe SARS-CoV-2 infection during the first wave of the pandemic. Clinical data were also recorded and analyzed. In case of findings supportive of myocardial inflammation, histological analysis was complemented by RT-PCR and immunohistochemistry for SARS-CoV-2 viral antigens and in situ RNA hybridization for the detection of viral genomes. RESULTS: Both chronic and acute myocardial damage was invariably present, correlating with the age and comorbidities of our population. Myocarditis of overt entity was found in one case (2.5%). SARS-CoV-2 genome was not found in the cardiomyocytes of the patient with myocarditis, while it was focally and negligibly present in cardiomyocytes of patients with known viral persistence in the lungs and no signs of myocardial inflammation. The presence of myocardial injury was not associated with myocardial inflammatory infiltrates. CONCLUSIONS: In this autopsy cohort of COVID-19 patients, myocarditis is rarely found and not associated with SARS-CoV-2 presence in cardiomyocytes. Chronic and acute forms of myocardial damage are constantly found and correlate with the severity of COVID-19 disease and pre-existing comorbidities.

Persistence of viral RNA, pneumocyte syncytia and thrombosis are hallmarks of advanced COVID-19 pathology.

BACKGROUND: COVID-19 is a deadly pulmonary disease with peculiar characteristics, which include variable clinical course and thrombophilia. A thorough understanding of the pathological correlates of the disease is still missing. METHODS: Here we report the systematic analysis of 41 consecutive post-mortem samples from individuals who died of COVID-19. Histological analysis is complemented by immunohistochemistry for cellular and viral antigens and the detection of viral genomes by in situ RNA hybridization. FINDINGS: COVID-19 is characterized by extensive alveolar damage (41/41 of patients) and thrombosis of the lung micro- and macro-vasculature (29/41, 71%). Thrombi were in different stages of organization, consistent with their local origin. Pneumocytes and endothelial cells contained viral RNA even at the later stages of the disease. An additional feature was the common presence of a large number of dysmorphic pneumocytes, often forming syncytial elements (36/41, 87%). Despite occasional detection of virus-positive cells, no overt signs of viral infection were detected in other organs, which showed non-specific alterations. INTERPRETATION: COVID-19 is a unique disease characterized by extensive lung thrombosis, long-term persistence of viral RNA in pneumocytes and endothelial cells, along with the presence of infected cell syncytia. Several of COVID-19 features might be consequent to the persistence of virus-infected cells for the duration of the disease. FUNDING: This work was supported by a King's Together Rapid COVID-19 Call grant from King's College London. MG is supported by the European Research Council (ERC) Advanced Grant 787971 "CuRE" and by Programme Grant RG/19/11/34633 from the British Heart Foundation.

Overview and Comparison of Infectious Endocarditis and Non-infectious Endocarditis: A Review of 814 Autoptic Cases.

AIM: We examined evidence on infective and non-infective endocarditis obtained from a database of 50,403 clinical autopsies performed at an Italian general hospital between January 1983 and December 2006. MATERIALS AND METHODS: Out of 814 endocarditis cases, 409 were of infective endocarditis (IE) and 405 non-infective (NIE). The median age at the time of death was 78 years for those with IE and 83 for those with NIE. Data were collected on gender, clinical history, comorbidities, kind of affected valve (non-prosthetic/mechanical/biological), pathological features of endocarditis, endocarditis complications and microbiological agents. RESULTS: The diagnosis of IE was frequently missed and these conditions were often complicated by cardiovascular events. IE was more common among patients with prior valve infection or cardiovascular surgery, while malignancies were frequent comorbidities of NIE. CONCLUSION: In general, we found several data that differ from those generally present in the scientific literature, and this could be explained by the fact that data on IE and NIE are generally obtained from surgical and clinical databases, while we analysed only autoptic cases.

Myocardial effects of fetal endoscopic tracheal occlusion in lambs with CDH.

INTRODUCTION: Fetal endoscopic tracheal occlusion in congenital diaphragmatic hernia (CDH) may reduce pulmonary hypertension and ameliorate postnatal cardiac output. The effects of sustained early (ETO) and late (LTO) tracheal occlusion on left ventricular (LV) cells in the lamb model have not been described. MATERIALS AND METHODS: CDH was created in lambs at 70 days' gestation (term = 145 days). ETO (85 days) or LTO (105 days) was sustained till term. After cesarean section (140 days) fetuses were euthanized and hearts harvested. LV myocardial cells were studied by histological and immunofluorescence (TGF-beta 1, endothelin-1) assays in CDH, ETO, LTO, and the control group (two subjects per group). Small intramyocardial arteries were evaluated by traditional histology. RESULTS: LV myocardial histology in CDH and LTO was similar. ETO-induced LV myocardial cell enlargement and increased endothelin-1 and TGF-beta 1 staining; a weaker immunofluorescence signal was observed in LTO compared with ETO. Myocardial vascular wall thickness was greater in CDH than in controls. ETO was associated with a vascular wall thickness within the range of controls. CONCLUSION: With only two fetuses in each group, only an explorative evaluation was possible. The time point at which TO is performed seems to have an effect on cardiac morphology. Functional studies as well as confirmation in clinical samples are mandatory.

Features of vulnerable plaques and clinical outcome of UA/NSTEMI: Relationship with matrix metalloproteinase functional polymorphisms.

OBJECTIVE: To assess the association of matrix metalloproteinases (MMP) genetic polymorphism (PM) with plaques vulnerability and clinical outcome of acute vascular events. METHODS: MMP-1 (-1607 G in/del), MMP-3 (-1171 A in/del), and MMP-9 microsatellite ((13-26) CA repeats around -90) PMs have been determined (i) in 204 patients with cerebrovascular disease to assess the association with features of vulnerability in carotid plaques and prevalence of stroke, (ii) in 208 patients with UA/NSTEMI to assess the association with in-hospital clinical outcome. RESULTS: Plaques from carriers of MMP-1 G insertion showed significantly smaller plaques and thicker fibrous cap. In CVD patients carrying such variant, Odds Ratio for previous stroke was 0.27 (95%C.I. 0.13-0.56, P=0.0002) and, in UA/NSTEMI patients, the risk of Major Adverse Cardiac Events (MACE, persistent angina, NSTEMI, and vascular death) was 0.22 (95%C.I. 0.11-0.44, P<0.0001). No variants in MMP-3 PM were associated to differences in either plaque features or clinical outcome. Carriers of MMP-9≥22 repeats in the microsatellite had larger plaques and lipid core. In CVD patients with such variant, Odds Ratio for stroke was 2.2 (95%C.I. 1.1-4.4) and, in UA/NSTEMI patients, MACE risk was 4.1 (95%C.I. 2.3-7.4, P<0.0001). Persistent angina and NSTEMI separately provided comparable results. CONCLUSIONS: Carriers of MMP-1 G insertion show smaller and more stable plaques, as well as better prognosis in acute vascular events, while patients with ≥22 repeats in MMP-9 have larger necrotic core and worse prognosis in UA/NSTEMI.

[Consensus document on endomyocardial biopsy of the Associazione per la Patologia Cardiovascolare Italiana]. / Documento di consenso sulla biopsia endomiocardica promosso dall'Associazione per la Patologia Cardiovascolare Italiana.

The Italian Scientific Associations of Cardiologists and Cardiovascular Pathologists have produced this consensus document on the diagnostic role of endomyocardial biopsy (EMB) in terms of techniques, analysis and reporting. The document is intended for clinical cardiologists, hemodynamic experts, electrophysiologists, surgical pathologists, and cardiac surgeons. It has three main aims: a) to collocate EMB in the context of currently available tools for diagnosis of heart diseases; b) to provide recommendations for rational implementation; c) to outline key characteristics (standards) for Italian cardiology and surgical pathology centers that perform and analyze EMB. A general lack of prospective, controlled studies addressing EMB prohibited the use of traditional evidence-based recommendations that rely on classes of available evidence. Thus, it was agreed that three key points should be taken into account: a) the specific pathology to be diagnosed (or excluded); b) the existence of any alternative, non-invasive diagnostic techniques; c) the overall consequences of reaching a definite diagnosis on patients' clinical management. Accordingly, we propose recommendations for EMB based on the following levels of diagnostic value: level 1: no alternative method exists to reach a definite diagnosis that can have obvious consequences for clinical management; level 2a: no alternative method exists to reach a definite diagnosis; however, the implications for clinical management are uncertain; level 2b: no alternative method exists to reach a definite diagnosis; however, the diagnosis would not influence clinical management; level 3: an alternative method exists to reach a definite diagnosis. The second part of the document proposes current protocols for the preparation, analysis and reporting of EMB in the context of each main pathologic entity. Particular attention is given to tissue characterization and implementation of molecular tests.

Apoptosis in patients with acute myocarditis.

Acute myocarditis is an acute inflammatory syndrome characterized by acute myocardial damage and dysfunction followed by a variable recovery over time with some patients progressing toward severe dilated cardiomyopathy. Cardiomyocyte apoptosis, a key pathologic feature of heart failure, may play a critical role in functional recovery in patients with acute myocarditis. The aim of the study was to investigate whether apoptosis predicts functional recovery in patients with acute myocarditis. Sixteen patients with biopsy-documented acute myocarditis were followed for 1 year with serial transthoracic echocardiography. Functional recovery was defined as 12-month left ventricular ejection fraction >40%. Cardiomyocyte apoptosis, leukocyte infiltration, and cell proliferation was assessed in all samples. A group of cases in which the diagnosis of acute myocarditis was made after death was also selected for comparison, and morphologically normal hearts from patients who died from a noncardiac cause were selected as controls. Six patients (38%) had functional recovery at 12 months, whereas 10 (62%) did not. The 2 groups had similar characteristics except for lower baseline left ventricular ejection fraction in the group with functional recovery. Apoptotic rate was found to be significantly higher in patients with acute myocarditis than in control hearts, and, unexpectedly, patients with functional recovery had significantly higher apoptotic rates than patients without recovery (3.2% vs 0.5%, p = 0.001). None of the patients with apoptotic rates below the median had functional recovery versus 86% of patients with apoptotic rates above the median (p <0.001). In conclusion, higher rates of cardiomyocyte apoptosis in patients with acute myocarditis are associated with functional recovery at 1 year.

Natural history of dilated cardiomyopathy: from asymptomatic left ventricular dysfunction to heart failure--a subgroup analysis from the Trieste Cardiomyopathy Registry.

BACKGROUND: Few data are available in the literature regarding the characteristics and prognosis of asymptomatic patients with idiopathic dilated cardiomyopathy (DCM). AIM: To determine the frequency with which patients affected by DCM are diagnosed in the asymptomatic state as well as to evaluate the natural history of such patients and the factors influencing their outcome. Moreover, we sought to compare the outcome of asymptomatic patients with that of patients with signs of overt heart failure at the time of first evaluation. METHODS AND RESULTS: We analyzed the data of 747 patients with DCM enlisted in the Heart Muscle Disease Registry of Trieste from 1978 to 2007. We divided our population into four groups; group 1 comprised 118 asymptomatic [New York Heart Association (NYHA) I] patients without a history of congestive symptoms (16%), group 2 comprised 102 asymptomatic (NYHA I) patients (14%) with a positive anamnesis for heart failure stabilized in medical therapy, group 3 comprised 327 patients (44%) with signs of mild heart failure (NYHA II) and group 4 comprised 200 patients (26%) in NYHA III-IV. During the follow-up of 112+/-63 months, 46 (21%) of 220 asymptomatic patients with DCM died or underwent heart transplantation. By Cox proportional model, left ventricular ejection fraction of 30% or less was a unique independent predictor either for death/heart transplantation (hazard ratio 3.15, 95% confidence interval 1.5-6.7, P=0.003) or for sudden death/major ventricular arrhythmias (hazard ratio 3.9, 95% confidence interval 1.7-9.3, P=0.002). Patients from group 1 had a trend for a better outcome with respect to those from group 2 (P=0.06). In comparison with the asymptomatic patients, those with signs of overt heart failure at baseline had a worse prognosis. CONCLUSION: The proportion of asymptomatic patients with DCM at the moment of first evaluation at our center is significant (30%). Among them, those without a previous history of heart failure had a less advanced disease and a trend for a better long-term outcome on optimal medical treatment. Therefore, early diagnosis may offer better long-term quality of life and even better survival. Further studies on larger populations are indicated.

Right ventricular cardiomyocyte apoptosis in patients with acute myocardial infarction of the left ventricular wall.

Cardiac remodeling after acute myocardial infarction (AMI) is characterized by molecular and cellular mechanisms involving both the left (LV) and right ventricular (RV) walls. Cardiomyoycte apoptosis in the peri-infarct and remote LV myocardium has a central role in cardiac remodeling. Whether apoptosis also occurs in the right ventricle of patients with ischemic heart disease has not been investigated. The aim of the present study was to investigate the presence of cardiomyocyte apoptosis in the right ventricle in patients with AMI. We assessed the number of apoptotic cardiomyocytes using multiple samplings in the LV and RV walls of 12 patients selected at autopsy who died 4 to 42 days after AMI. Five patients without cardiac disease were also selected at autopsy as controls. Apoptotic rates were calculated from the number of cardiomyocytes showing double positive staining for in situ end-labeling of DNA fragmentation (TUNEL) and for activated caspase-3. Potentially false-positive results (DNA synthesis and RNA splicing) were excluded from cell counts. The apoptotic rate in the right ventricle in patients with AMI was significantly higher than in control hearts (median 0.8%, interquartile range 0.3 to 1.0 vs median 0.01%, interquartile range 0.01 to 0.03, p <0.001). RV apoptosis significantly correlated with such parameters of global adverse remodeling as cardiac diameter to LV free wall thickness (R = +0.57, p = 0.050). RV apoptosis was significantly higher in five cases (42%) with infarct involving the ventricular septum and an adjacent small area of the RV walls (median 1.0%, interquartile range 0.8 to 2.2 vs median 0.5%, interquartile range 0.2 to 1.0, p = 0.048, p <0.001 vs controls). The association between apoptotic rate in the right ventricle and cardiac remodeling was apparent even after exclusion of cases with RV AMI involvement (R = +0.82, p = 0.023 for diameter to LV wall thickness ratio and R = -0.91, p = 0.002 for RV free wall thickness). In conclusion, patients with cardiac remodeling after AMI had a significant increase in RV apoptosis even when ischemic involvement of the RV wall was not apparent.

The challenge of cardiomyopathies in 2007.

The last 20 years have seen impressive progress in the study of cardiomyopathies. The improved understanding of these diseases has made clear that cardiomyopathies are extremely complex entities that defy current classification standards. The 1980 and 1995 WHO/ISFC Task Forces, and very recently an American Heart Association (AHA) Scientific Statement expert panel, have systematically approached new advances as well as emerging problems. In spite of this effort and an increasingly growing understanding of myocardial disorders, several issues remain unresolved. Without a doubt, the identification of genetic defects responsible for many forms of cardiomyopathies has changed our perspective of myocardial diseases. In fact, in the last few years, we have seen that (1) clinically defined cardiomyopathies, previously considered single entities, are actually the result of mutations in different genes, (2) different mutations in the same gene may be the cause of different clinical entities and (3) in the group of cardiomyopathies, a large phenotypic and genetic heterogeneity exists that is expected to increase in the future. Genotype knowledge is a fundamental advance in medicine and in particular in the field of cardiomyopathies and is becoming increasingly more important in clinical practice for disease diagnosis and prevention, prognostic stratification and possible future therapies. Knowledge of the phenotype, including clinical, morphological and physiological features, however, continues to provide the clinical basis for diagnosis and classification of cardiomyopathies, prognostic evaluation and symptomatic treatment, and should not be abandoned.

Arrhythmogenic right ventricular dysplasia/cardiomyopathy as a cause of sudden infant death.

Arrhythmogenic right ventricular dysplasia/cardiomyopathy is a rarely described cause of sudden death among infants. We report the case of a 4-month-old male infant who died suddenly in his sleep. Postmortem examination revealed the presence of arrhythmogenic right ventricular dysplasia/cardiomyopathy.

Identification of protein disulfide isomerase as a cardiomyocyte survival factor in ischemic cardiomyopathy.

OBJECTIVES: The aim of the study was to analyze the molecular mechanisms activated during postinfarction remodeling in human hearts. BACKGROUND: The molecular mechanisms of initial response to ischemic insult in the heart and the pathways involved in compensation and remodeling are still largely unknown. METHODS: Up-regulation or down-regulation of gene expression in the human viable peri-infarct (vs. remote) myocardial region was investigated by complementary deoxyribonucleic acid array technology and confirmed at a single-gene/protein level with reverse transcriptase polymerase chain reaction and immunohistochemistry. An in vitro model of cardiomyocyte hypoxia in HL1 cells was used to validate anti-apoptotic effects of the candidate gene/protein and to assess the associated downstream cascade. Finally, a mouse model of myocardial infarction was used to test the in vivo effects of exogenous transfection with the candidate gene/protein. RESULTS: Protein disulfide isomerase (PDI), a member of the unfolded protein response, is 3-fold up-regulated in the viable peri-infarct myocardial region, and in a postmortem model, its expression is significantly inversely correlated with apoptotic rate and with presence of heart failure (HF) and biventricular dilatation. Induced PDI expression in HL1 cells conferred protection from hypoxia-induced apoptosis. Adenoviral-mediated PDI gene transfer to the mouse heart resulted in 2.5-fold smaller infarct size, significantly reduced cardiomyocyte apoptosis in the peri-infarct region, and smaller left ventricular end-diastolic diameter versus mice treated with a transgene-null adenoviral vector. CONCLUSIONS: These results suggest that PDI promotes survival after ischemic damage and that zinc-superoxide dismutase is one of the PDI molecular targets. Pharmacological modulation of this pathway might prove useful for future prevention and treatment of HF.

Left ventricular diastolic filling pattern at Doppler echocardiography and apoptotic rate in fatal acute myocardial infarction.

Heart failure is a complex syndrome characterized by impaired emptying and/or impaired filling of the heart chambers. The use of parameters of diastolic function has provided novel tools for risk stratification and management of patients with heart failure. This study evaluated the potential correlation between apoptosis at time of death and left ventricular (LV) diastolic function after acute myocardial infarction. We selected, at routine postmortem examination, 14 subjects who died 10 to 62 days after an acute myocardial infarction and had an available echocardiographic report from the most recent hospital admission. The apoptotic rate was calculated at the region bordering the infarct, using co-localization of in situ end-labeling for deoxyribonucleic acid fragmentation and immunohistochemistry for caspase-3. Transthoracic echocardiographic studies were retrospectively reevaluated and pulse-wave Doppler spectra of mitral inflow were analyzed. LV diastolic function was assessed by measuring the ratio of E peak velocity to A peak velocity and E-wave deceleration time; a ratio of E peak velocity to A peak velocity >or=2 and deceleration time <115 ms were considered a restrictive filling pattern. A restrictive pattern was found in 4 cases (29%). All subjects with a restrictive pattern were symptomatic for New York Heart Association class IV heart failure (100% vs 20%, p = 0.015) and had larger transverse heart diameters at pathology (p = 0.014). The apoptotic rate in the peri-infarct region was significantly higher in patients with a restrictive versus nonrestrictive diastolic pattern (13%, 10 to 14, vs 3%, 1 to 6, p = 0.014). At multivariable analysis that included the restrictive pattern, class IV heart failure, and cardiac diameters, the restrictive pattern remained an independent predictor of increased apoptosis (p = 0.030). In conclusion, patients with severe postinfarction LV diastolic dysfunction had significantly higher rates of cardiomyocyte loss by apoptosis, which may partly explain their unfavorable outcome.

Infarct-related artery occlusion, tissue markers of ischaemia, and increased apoptosis in the peri-infarct viable myocardium.

AIMS: Unfavourable cardiac remodelling often complicates acute myocardial infarction (AMI) as a result of increased cardiomyocyte apoptosis. It is currently unclear whether ongoing or recurrent ischaemia is an independent determinant for increased apoptosis in peri-infarct viable myocardium. METHODS AND RESULTS: In order to assess the link between infarct-related artery (IRA) occlusion, ischaemia, and apoptosis, 30 subjects dying 7-120 days after AMI (16 with IRA occlusion and 14 with patent IRA) and five control subjects were selected at autopsy. Cardiomyocytes were defined as apoptotic if co-expressing TUNEL and activated caspase-3. Expression of both hypoxia-inducible factor-1 and cyclo-oxygenase-2 was assessed in the peri-infarct myocardium and considered as tissue markers of ischaemia. Evidence of ischaemia was significantly more frequent in cases with IRA occlusion (53%) than in cases with patent IRA (15%) or control hearts (0%, P=0.026). The finding of IRA occlusion and markers of ischaemia identified cases with higher apoptotic rates (ARs) in the peri-infarct viable myocardium [12.2% (8.2-14.0), P<0.001 vs. others], whereas IRA occlusion without ischaemia was associated with lower AR, not significantly different from patent IRA [3.0% (1.0-7.9) vs. 2.2% (1.0-5.8), respectively, P=0.42] CONCLUSION: Ischaemia in the peri-infarct viable myocardium is present in over 50% of subjects dying late after AMI with IRA occlusion, and it is associated with increased apoptosis. Relief of ischaemia after AMI may prove of benefit in preventing apoptosis and its consequences.

Myocardial regeneration by activation of multipotent cardiac stem cells in ischemic heart failure.

In this study, we tested whether the human heart possesses a cardiac stem cell (CSC) pool that promotes regeneration after infarction. For this purpose, CSC growth and senescence were measured in 20 hearts with acute infarcts, 20 hearts with end-stage postinfarction cardiomyopathy, and 12 control hearts. CSC number increased markedly in acute and, to a lesser extent, in chronic infarcts. CSC growth correlated with the increase in telomerase-competent dividing CSCs from 1.5% in controls to 28% in acute infarcts and 14% in chronic infarcts. The CSC mitotic index increased 29-fold in acute and 14-fold in chronic infarcts. CSCs committed to the myocyte, smooth muscle, and endothelial cell lineages increased approximately 85-fold in acute infarcts and approximately 25-fold in chronic infarcts. However, p16(INK4a)-p53-positive senescent CSCs also increased and were 10%, 18%, and 40% in controls, acute infarcts, and chronic infarcts, respectively. Old CSCs had short telomeres and apoptosis involved 0.3%, 3.8%, and 9.6% of CSCs in controls, acute infarcts, and chronic infarcts, respectively. These variables reduced the number of functionally competent CSCs from approximately 26,000/cm3 of viable myocardium in acute to approximately 7,000/cm3 in chronic infarcts, respectively. In seven acute infarcts, foci of spontaneous myocardial regeneration that did not involve cell fusion were identified. In conclusion, the human heart possesses a CSC compartment, and CSC activation occurs in response to ischemic injury. The loss of functionally competent CSCs in chronic ischemic cardiomyopathy may underlie the progressive functional deterioration and the onset of terminal failure.