RESUMEN
Pericardial defects are considered rare in animals and humans. Pericardial agenesis is characterized by partial or total pericardial sac malformation. Here is reported a case of apical partial pericardial agenesis in an adult mixed-breed male dog referred for necropsy. The pericardial sac was absent from the apical region up to the middle area of the ventricles resulting in a bilateral ventricular compression by the remaining pericardium changed the organ conformation. Microscopically, there was evidence of neutrophilic and hemorrhagic myocarditis with cardiomyocyte atrophy and interstitial fibrosis. Agenesis is often a subclinical disorder, and it is an incidental postmortem finding in most cases; however, it can cause complications in cases of cardiac structure herniation.(AU)