Exposure of humans to the zoonotic nematode Dirofilaria immitis in Northern Portugal.

Dirofilariosis caused by Dirofilaria immitis (heartworm) is a zoonosis, considered an endemic disease of dogs and cats in several countries of Western Europe, including Portugal. This study assesses the levels of D. immitis exposure in humans from Northern Portugal, to which end, 668 inhabitants of several districts belonging to two different climate areas (Csa: Bragança, Vila Real and Csb: Aveiro, Braga, Porto, Viseu) were tested for anti-D. immitis and anti-Wolbachia surface proteins (WSP) antibodies. The overall prevalence of seropositivity to both anti-D. immitis and WSP antibodies was 6.1%, which demonstrated the risk of infection with D. immitis in humans living in Northern Portugal. This study, carried out in a Western European country, contributes to the characterisation of the risk of infection with D. immitis among human population in this region of the continent. From a One Health point of view, the results of the current work also support the close relationship between dogs and people as a risk factor for human infection.

Presumptive primary intrathoracic mast cell tumours in two dogs.

BACKGROUND: Mast cell tumours are the most common cutaneous neoplasms in dogs. Other primary sites include visceral organs, such as the gastrointestinal tract, liver, or spleen, and the oral cavity. Frequent metastatic sites include the local lymph nodes, skin, spleen, liver and bone marrow. The thorax is rarely affected by metastatic disease and no such cases have been reported in dogs. Mast cell tumours are usually not considered as a differential diagnosis for lung and intrathoracic chest wall masses in dogs. Chest wall tumours can be primary tumours of the ribs and sternum, an invasion of adjacent tumours into the chest wall, and metastasis from distant tumours. CASES PRESENTATION: A German Shepherd dog presented with a history of persistent cough and a large mass involving the thoracic wall and a small round pulmonary mass. The dog had a history of mammary tumours that were surgically excised. Thoracoscopy revealed a thoracic wall mass involving the internal intercostal muscle and a small mass in the left cranial lung lobe. Cytology and histopathology of the intrathoracic mass confirmed the large mass as a mast cell tumour and the small mass as a carcinoma. Cytology of the sternal lymph nodes showed no involvement. The dog received toceranib for 3 months, which failed to alleviate persistent cough. Radiology indicated that the large mass had a partial response to toceranib. The dog was euthanasied. A Maltese dog presented with a history of chronic regurgitation and cough, and a large mass involving the left caudal lung lobe. Cytology and histopathology of mass confirmed a mast cell tumour. The dog received toceranib for 2 months. Radiology indicated that the large mass had no response to toceranib. The dog was euthanasied. Confirmation of lungs mast cell tumour and the absence of any other Mast cell tumour was achieved by postmortem examination. CONCLUSIONS: The cases discussed are two unusual presentations of intrathoracic mast cell tumours, in the absence of cutaneous mast cell tumours, in dogs.

Stray Dogs of Sofia (Bulgaria) Could be an Important Reservoir of Heartworm (Dirofilaria Immitis).

Dirofilaria immitis (heartworm) is a zoonotic and an emerging disease, expanding in Europe. In Bulgaria, the presence of the parasite has been described in many regions. However, canine heartworm has hardly been evaluated in the capital of the country and, therefore, the aim of this study was to evaluate the prevalence and distribution of canine heartworm in Sofia. Eighty stray dogs from the city of Sofia and the metropolitan area were analysed for circulating D. immitis antigens. The prevalence was 31.25 %, being 34.7 % in the metropolitan area and 25.8 % in the city of Sofia. The current results are among the highest reported in the country. This could be due to the lack of prophylactic measures against infection in these dogs, but also to the spread of D. immitis into non-endemic countries. Stray dogs may act as an important reservoir of heartworm being a risk for client-owned animals and for the development of pulmonary dirofilariosis in inhabitants. The results show the need to establish further epidemiological studies and prophylactic campaigns for stray and client-owned animals, as well as to create awareness campaigns about the severity and importance of this disease for both animals and humans.

The Canary Islands as a model of risk of pulmonary dirofilariasis in a hyperendemic area.

We assessed the risk of human pulmonary dirofilariasis in the Canary Islands, hyperendemic for canine heartworm (Dirofilaria immitis), a zoonotic vector-borne infection. For this purpose, 1479 inhabitants were tested for anti-D. immitis antibodies. Four of the 7 islands presented high seroprevalences (from 6.2 to 12.7%), therefore high exposure to the parasite and risk of zoonotic infection. These corresponded to those islands with high canine prevalences of dirofilariasis and favourable climatic conditions for the development of mosquito vectors. The lowest prevalences (from 0 to 1.6%) were found in the desert islands and those with low canine prevalences of heartworm. Seroprevalences were very variable inside each island as well, being related to the climate and demographic factors. Human pulmonary dirofilariasis is an emerging zoonosis worldwide which frequently goes undiagnosed. Serological studies could be useful for the correct evaluation of the risk of infection among the human population, and study of the health implications of the continuous contact with the parasite in endemic areas. Sanitary authorities should be aware of the current epidemiological data, and physicians should include human dirofilariasis in the differential diagnosis of pulmonary nodules.

Broader conceptualization of remission assessed by the remission from depression questionnaire and its association with symptomatic remission: a prospective, multicenter, observational study.

BACKGROUND: Goals of treating major depressive disorder (MDD) include achieving remission and avoiding relapse. It is possible that patients may have a broader view of remission than what is captured via clinician-rated scales. This patient perspective may, in turn, have an impact on treatment outcomes. METHODS: The association between a broader conceptualization of remission, based on the Remission from Depression Questionnaire (RDQ) score at baseline, and being in symptomatic remission after 6 months was evaluated in subjects (N = 613) with MDD in symptomatic remission at baseline (17-item Hamilton Rating Scale for Depression [HAMD-17] ≤7). Specific aspects of depression were assessed from physician and patient perspectives as secondary endpoints. A backwards selection strategy was used to statistically model remission status and determine association of factors with potential to influence remission. RESULTS: At month 6, after adjustment for baseline HAMD-17 score, there was no association between baseline RDQ score and symptomatic remission status (HAMD-17), relapse, composite remission status, healthcare resource utilization, or quality of life. There was no association between functional impairment scores at baseline (Sheehan Disability Scale and Social and Occupational Functioning Assessment Scale) and symptomatic remission status (HAMD-17) at month 6. CONCLUSIONS: This study indicates that RDQ-constructs are independent from symptomatic remission. Symptom severity at study entry appeared to be the only significant predictor of eventual relapse during the 6-month follow-up period. However, our results also suggest that the current definition of remission that is based on symptom reduction should be further elaborated and that alternative or additional definitions should be considered in determining remission.

Rectal pre-treatment with ozonized oxygen (O3) aggravates clinic status in septic rats treated with amoxicillin/clavulanate.

INTRODUCTION: Despite the advanced antibiotic therapies, sepsis continues being a clinical entity with high morbidity and mortality. The ozone/oxygen mixture (O3/O2) has been reported to exhibit positive effects on immunity. The aim of our study was to analyze whether (O3/O2) combined with amoxicillin/clavulanate has any influence on the morbidity and mortality of septic rats. METHODS: We used 48 Sprague-Dawley rats randomly allocated to 6 groups (n=8): healthy (C), septic (I), healthy+ozone therapy (O3), septic+amoxicillin/clavulanate (AMC), septic+amoxicillin/clavulanate+ozone therapy (AMC/O3) and septic+ozone therapy (I/O3). O3/O2 was administered rectally at increasing O3 concentrations during 10 days prior to the onset of sepsis model (intraperitoneally injection of fecal material) or saline administration in healthy control rats. Later (post-inoculation), 3 days per week, O3 was also administered. Vital signs were recorded, and microbiological, hematological and histopathological studies were performed. RESULTS: The number of surviving animal/total was higher in AMC (8/8) than in AMC/O3 (4/8) p=0.077. The percentage of surviving animals with pneumonia was higher in AMC/O3 than in AMC (100% vs 37.5%). In dead animals, AMC/O3 rats had a significantly higher percentage of lesions: Cardiac lesions, pulmonary hemorrhages and pleuritis (100%) and serositis/peritonitis (75%). Only Escherichia coli (2 different biotypes) was isolated from blood and/or peritoneal fluid from all infected groups. A significant decrease in the percentage of band neutrophils from the surviviors belonging to AMC/O3vs AMC was observed (p<0.05). CONCLUSION: Rectal pre-treatment with O3/O2 aggravates clinic status in septic rats treated with amoxicillin/clavulanate.

Seroprevalence of heartworm (Dirofilaria immitis) in feline and canine hosts from central and northern Portugal.

Dirofilaria immitis is endemic in Portugal. Several studies have reported the presence of canine heartworm disease, although no previous studies on feline infections have been published. The aim of this study was to determine the prevalence of D. immitis in cats and dogs from central and northern Portugal. Blood samples from 434 cats were tested for circulating anti-D. immitis and anti-Wolbachia antibodies. Furthermore, 386 dogs were tested for circulating D. immitis antigens. Overall feline seroprevalence was 15%, while canine prevalence was 2.1%. The highest feline seroprevalences of 18.7% and 17.6% were found in Aveiro and Viseu, respectively, while the highest canine prevalences of 8.8% and 6.8% were found in Coimbra and Aveiro, respectively. Cats and dogs showing respiratory signs presented higher prevalences of 24.4% and 17%, respectively, while 50% of cats with gastrointestinal signs were seropositive. The present study confirms the seropositivity of D. immitis in the feline population in central and northern Portugal, and suggests the importance of including heartworm disease in the list of differential diagnoses of cats and dogs showing clinical signs compatible with the disease.

Human and animal dirofilariasis: the emergence of a zoonotic mosaic.

Dirofilariasis represents a zoonotic mosaic, which includes two main filarial species (Dirofilaria immitis and D. repens) that have adapted to canine, feline, and human hosts with distinct biological and clinical implications. At the same time, both D. immitis and D. repens are themselves hosts to symbiotic bacteria of the genus Wolbachia, the study of which has resulted in a profound shift in the understanding of filarial biology, the mechanisms of the pathologies that they produce in their hosts, and issues related to dirofilariasis treatment. Moreover, because dirofilariasis is a vector-borne transmitted disease, their distribution and infection rates have undergone significant modifications influenced by global climate change. Despite advances in our knowledge of D. immitis and D. repens and the pathologies that they inflict on different hosts, there are still many unknown aspects of dirofilariasis. This review is focused on human and animal dirofilariasis, including the basic morphology, biology, protein composition, and metabolism of Dirofilaria species; the climate and human behavioral factors that influence distribution dynamics; the disease pathology; the host-parasite relationship; the mechanisms involved in parasite survival; the immune response and pathogenesis; and the clinical management of human and animal infections.

Successful Transvenous Extraction of Adult Dirofilaria immitis Parasites from a Naturally Infected Domestic Ferret (Mustela putorius furo).

Heartworm disease caused by Dirofilaria immitis is a serious and underdiagnosed cardiovascular condition in domestic ferrets. Hemodynamic changes caused by parasitization in ferrets cause a potentially fatal syndrome, but its clinical findings and treatment have not yet been standardized. The objective of this study was to describe the clinical case of a successful surgical extraction in a ferret infected by D. immitis. The patient was a 2-year-old, 1.5 kg asymptomatic male domestic ferret. The infection was diagnosed using a commercial test for the detection of D. immitis antigens. Subsequently, their clinical status was evaluated using serological and imaging diagnostic tests, and it was finally decided to perform surgical extraction of the adult worms. The ferret was anesthetized and placed in the left lateral decubitus position to perform a venotomy in the right jugular vein. Endoscopic extraction basket-shaped devices were used in the right atrial cavity under fluoroscopic guidance following the Seldinger endovascular surgery technique. With careful handling, two adult parasites were manually removed. A transthoracic echocardiogram performed after the procedure confirmed the absence of heartworms. The ferret recovered without complications and was discharged within 24 h. In the clinical review, 30 days after surgery, no notable alterations or symptoms were observed. This case report describes the first complete surgical removal of adult D. immitis parasites in a naturally infected ferret.

Assessment of Thoracic Radiographic Alterations in Dogs with Heartworm and Their Correlation with Pulmonary Hypertension, Pre- and Post-Adulticide Treatment.

Pulmonary hypertension (PH) is a prevalent and severe complication in dogs infected with Dirofilaria immitis. This study aimed to elucidate the progression of PH by analyzing radiographic parameters and the Right Pulmonary Artery Distensibility (RPAD) Index at three key time points: diagnosis (day 0), discharge (day 90), and six months post-discharge (day 270). Fifty-two heartworm-infected dogs were divided into two groups: non-hypertensive and hypertensive. Radiographic measurements, including Vertebral Heart Size (VHS), CrPA/R4 ratio, and CdPA/R9 ratio, along with the RPAD Index, were assessed on Days 0, 90, and 270. Results indicated that, in Group A, the RPAD Index improved significantly from 42% on Day 0 to 43.16% on Day 90, with no significant change by Day 270 (42%). In contrast, hypertensive dogs exhibited a persistently low RPAD Index, averaging 17% throughout this study (p < 0.001). Radiographic parameters in hypertensive dogs showed continuous elevation compared to non-hypertensive dogs, with significant increases in VHS, CrPA/R4, and CdPA/R9 ratios on day 270 compared to day 0 (p < 0.05). The results confirmed that PH persisted in dogs with D. immitis after adulticide treatment, highlighting the importance of regular radiographic monitoring for assessing and managing long-term outcomes in dogs with PH during and after adulticide treatment. Continuous surveillance is thus essential for the effective post-treatment management of PH in dogs.

Association between Thoracic Radiographic Changes and Indicators of Pulmonary Hypertension in Dogs with Heartworm Disease.

Pulmonary hypertension (PH) is a consequence of pulmonary endarteritis during infection with Dirofilaria immitis in dogs. Echocardiography is the technique of choice but is not always accessible to all clinicians. This study aimed to evaluate the association of the radiological findings in dogs with heartworm disease and the presence or absence of echocardiographically characterised PH. The study included 62 heartworm-infected dogs that underwent thoracic radiographs and echocardiography. The studied dogs showed moderate to severe PH when the Right Pulmonary Artery Distensibility (RPAD) Index was <29.5%. The RPAD Index was used for comparison with thoracic radiographs. The Vertebral Heart Size (VHS), right cranial pulmonary artery passing through the fourth rib in the laterolateral projection (CrPA/R4) ratio, and right caudal pulmonary artery to the ninth rib in the dorsoventral projection (CdPA/R9) ratio showed significant differences between dogs with/without PH (p < 0.001). Sensitivity (sen) and specificity (sp) cut-off values were obtained: VHS ≥ 9.53 (sen 93.75%, sp 63.33%); CrPA/R4 ≥ 1.08 (sen 87.5%, sp 70%); and CdPA/R9 ≥ 1.10 (sen 96.88%, sp 76.66%). The CrPA/R4 and CdPA/R9 ratios showed potential as a preliminary screening tool for PH in heartworm-infected dogs, suggesting that they may reliably indicate the presence of PH and guide the decision for further diagnostic testing.

Change in the Distribution Pattern of Dirofilaria immitis in Gran Canaria (Hyperendemic Island) between 1994 and 2020.

Dirofilariosis is a zoonotic disease that mainly affects dogs and cats, with a high risk to public health. The island of Gran Canaria (Spain) has been shown to be a hyperendemic area of infection and, therefore, a model for studying the evolution of the disease. The objective of this study was to track the prevalence and distribution of heartworm in dogs, cats, and residents of Gran Canaria from 1994 to 2020, using published and unpublished data. Blood samples from 5841 dogs, 1203 cats, and 1604 humans were collected in the years analyzed, considering geographical and isoclimatic factors. In 1994, a prevalence of Dirofilaria immitis of 67.02% in dogs was reported, while in 2020 it was 15.81%. In cats, the seroprevalence in 2010 was 33.03%, compared to 17.20% in 2020. The incidence of D. immitis in humans in 2008 was 18.66%, while in 2020 it was 8.27%. For all study groups, temperate cold zone (TC) and temperate mild zone (TM) climates had the highest prevalence. Throughout these 20 years, the prevalence of heartworm disease has decreased. Despite this, it continues to be a hyperendemic island. This study highlights the importance of using the "One Health" perspective and the risks of contagion of the disease.

Machine Learning Techniques for Canine Myxomatous Mitral Valve Disease Classification: Integrating Anamnesis, Quality of Life Survey, and Physical Examination.

Myxomatous mitral valve disease (MMVD) is a prevalent canine cardiac disease typically diagnosed and classified using echocardiography. However, accessibility to this technique can be limited in first-opinion clinics. This study aimed to determine if machine learning techniques can classify MMVD according to the ACVIM classification (B1, B2, C, and D) through a structured anamnesis, quality of life survey, and physical examination. This report encompassed 23 veterinary hospitals and assessed 1011 dogs for MMVD using the FETCH-Q quality of life survey, clinical history, physical examination, and basic echocardiography. Employing a classification tree and a random forest analysis, the complex model accurately identified 96.9% of control group dogs, 49.8% of B1, 62.2% of B2, 77.2% of C, and 7.7% of D cases. To enhance clinical utility, a simplified model grouping B1 and B2 and C and D into categories B and CD improved accuracy rates to 90.8% for stage B, 73.4% for stages CD, and 93.8% for the control group. In conclusion, the current machine-learning technique was able to stage healthy dogs and dogs with MMVD classified into stages B and CD in the majority of dogs using quality of life surveys, medical history, and physical examinations. However, the technique faces difficulties differentiating between stages B1 and B2 and determining between advanced stages of the disease.

Current State of Canine Heartworm in Portugal.

The favourable geo-climatic conditions in Portugal have made it highly conducive to the development of Dirofilaria immitis in dogs, leading to its identification as an endemic region. This nematode is rapidly spreading across Europe, particularly in northeastern countries. The objective of this study was to provide an updated assessment of the prevalence of this disease in Portuguese dogs, analysing the results in relation to epidemiological and geo-environmental factors, and to identify potential risk factors. A total of 1367 dogs from all continental and insular districts were included in the study and tested for D. immitis antigens. The overall prevalence was found to be 5.9%. It was observed that the disease is spreading northward, with previously unaffected districts now reporting cases, and that the prevalence in coastal districts exceeded that of inland ones. Notably, the Aveiro district exhibited a significant increase in D. immitis prevalence, while in certain districts such as Setúbal, Santarém, Madeira, or Faro, a stabilisation or decrease in prevalence was noted. Furthermore, outdoor and older dogs were found to be at a higher risk of infection. No positive cases were detected in the Azores. Most of the infected dogs were located in areas of high and medium risk of infection. This study underscores the importance of implementing pharmacological prophylaxis, vector control strategies, and public awareness programs to control the spread of this zoonotic disease.

Long-term quality-of-life and functioning comparison of atomoxetine versus other standard treatment in pediatric attention-deficit/hyperactivity disorder.

Psychopharmacological agents were shown to be important for improving the quality of life (QoL) of patients with attention-deficit/hyperactivity disorder (ADHD). A short-term, 10-week study found atomoxetine (ATX) to be effective in improving QoL of ADHD patients. We compared, for the first time, long-term treatment outcomes of ATX and other early standard therapy (OEST, any pharmacological ADHD treatment except ATX) in QoL and functional impairment in pharmacologically naive children/ adolescents in a randomized, controlled, open-label study at 6 and 12 months. Patients received ATX (0.5-1.8 mg/kg per day) or OEST (mainly methylphenidate). Quality of life and functioning were assessed by the Child Health and Illness Profile-Child Edition, Parent Rating Form and the Weiss Functional Impairment Rating Scale-Parent Report. Three hundred ninety-eight patients (79.4% male; mean age, 9.3 years) received study treatment. The Child Health and Illness Profile-Child Edition, Parent Rating Form achievement domain t scores significantly improved from baseline to 6 months from means of 28.0 to 37.1 for ATX and from 28.3 to 40.7 for OEST. Mean t scores at 12 months were 40.0 for ATX and 41.0 for OEST. The Weiss Functional Impairment Rating Scale-Parent Report total score improved from baseline to 6 months in both groups (ATX: mean 1.02 to 0.63; OEST: 0.96 to 0.59). Both treatments were safe with no statistically significant difference in the overall rate of adverse events. Overall, the improvements in QoL and functional impairment observed over time for ATX and OEST were meaningful and stable over the study period of 12 months. Between-group differences were small but sometimes statistically significant, providing the first-time long-term comparative symptomatic and QoL analysis between ATX and OEST.

Evaluating Internet information on attention-deficit/hyperactivity disorder (ADHD) treatment: parent and expert perspectives.

BACKGROUND: The Internet is increasingly used as a source of health-related information. The objective of this study was to assess the quality of web-based information on treatments for attention-deficit/hyperactivity disorder (ADHD). METHODS: Sixteen expert health professionals in ADHD and 35 parents of paediatric patients with a recent diagnosis of ADHD assessed the information contained in the 10 highest ranked websites in Spanish, using the Spanish version of the DISCERN tool - a validated questionnaire designed to assess the quality and reliability of web-based information on treatment choices (rating scores from 15 to 75). RESULTS: DISCERN scores given by parents and experts were low (total mean scores [standard deviation]: 35.9 [13.1] and 43.4 [13.7], respectively) and inter-rater agreement was poor/moderate (weighted kappa for the global assessment between -0.69 and +0.93, average = 0.29). There was a significant change on the ADHD-knowledge and motivation for treatment (ADHD-KMT) basic knowledge sub-scale score after the assessment of the different websites by parents (total mean scores [standard deviation]: 49.09 [9.46] and 63.21 [9.45]). CONCLUSIONS: Despite a poor/moderate inter-rater agreement between parent and expert opinions, all agreed that the quality of the web-based information on treatment choices for ADHD is generally poor.

Radiographic Left Atrial Size Measurement of Dogs in Different Mitral Valve Disease Stages with Four Different Methods.

The left atrial size increases (LAS) in patients with mitral valve disease (MVD) as the disease progresses. The vertebral left atrial size (VLAS), the modified-vertebral left atrial size (M-VLAS), and the radiographic left atrial dimension (RLAD) are methods reported to assess LAS on dogs' radiographs. All these methods transform the LAS into vertebral units. The thoracic inlet (TI) has been used as a reliable reference point to measure the cardiac silhouette of dogs with MVD in different stages. The objective of this study was to assess the clinical utility of measuring a dog LAS on right thoracic X-rays using the TI as a reference and determine whether it could differentiate dogs in different MVD stages. LAS was divided by the TI to obtain the thoracic inlet left atrial score (TILAS). This was a retrospective observational study including 135 apparently healthy dogs performed to assess their LAS with four different methods: VLAS, M-VLAS, RLAD, and TILAS. Thirty-six dogs from the general population were selected and compared to 100 dogs in different MVD stages. The TILAS was significantly different between the control dogs and MVD dogs, increasing with the disease stage: control dogs 0.51 ± 0.08, B1 0.57 ± 0.14, B2 0.75 ± 0.13, and C 0.84 ± 0.18. VLAS, M-VLAS, and RLAD also increased as the disease progressed, as shown in previous studies. The TILAS accuracy to distinguish MVD dogs with cardiac enlargement was comparable to VLAS, M-VLAS, and RLAD (AUC 0.91 vs. 0.93, 0.90, and 0.94 respectively). A TILAS > 0.8 can identify dogs with cardiac enlargement secondary to MVD.

The Thoracic Inlet Length as a Reference Point to Radiographically Assess Cardiac Enlargement in Dogs with Myxomatous Mitral Valve Disease.

The diagnostic value of the vertebral heart size (VHS) in dogs with mitral valve degeneration (MVD) is compromised when middle thoracic vertebral anomalies are present. The objective of this study was to assess the use of the thoracic inlet heart score (TIHS) to identify left heart enlargement (LHE) secondary to MVD. The cardiac silhouette of 50 clinically healthy dogs and 106 MVD dogs in different stages was assessed on a right lateral chest radiograph. The TIHS and VHS value were calculated for each patient and compared. The TIHS was significantly different between the control dogs and the dogs with MMVD, increasing with disease stage, control 2.91 ± 0.23, Stage B1 2.98 ± 0.36, B2 3.25 ± 0.34, and C 3.53 ± 0.36, p < 0.05. A THIS ≥3.3 showed 69% sensitivity and 81% specificity to identify LHE. The TIHS showed moderate correlation with the VHS, LA/Ao, and LVIDDN 0.59, 0.42, and 0.62, respectively. The intraobserver and interobserver agreement were almost perfect, 0.96, and substantial, 0.73. The TIHS method can be used to identify LHE secondary to MMVD on dogs' thoracic radiographs.

The Thoracic Inlet Heart Size, a New Approach to Radiographic Cardiac Measurement.

In 1995, the Vertebral Heart Size (VHS) method for measuring the cardiac silhouette on thoracic radiographs was published, becoming a quantifiable and objective reference way of assessing the heart size. Since then, many studies have showed that VHS is influenced by breed variations, vertebral malformations, reference points selection, and short and long axes dimensions conversion into vertebral units. The Thoracic Inlet Heart Size (TIHS) normalizes heart size to body size using the thoracic inlet length. The lengths of the long and short axes of the heart of 144 clinically normal dogs were measured on right lateral thoracic radiographs. The sum of both measures was indexed to the thoracic inlet length. For comparison, dogs of the most represented breeds in our hospital were selected to measure their heart size using the TIHS protocol. The mean TIHS value for the population studied was 2.86 ± 0.27, and 90% of dogs had a TIHS value of less than 3.25. There was no difference in TIHS between male and female, and between small and large dogs (p-value < 0.01). There was no difference in the TIHS value between Yorkshire Terrier, Chihuahua, and Labrador retriever breeds, and between each of those three breeds and the general population. The TIHS is a simple, straightforward and accurate way to measure heart size.