The available information on the cardiovascular apparatus of the capybara (Hydrochoerus hydrochaeris) is scarce. The general objective of this study was to describe the cardiac anatomy of this species. Six adult animals and five newborns were used; all were free of cardiovascular system pathologies. The method of study of the animals was simple dissection. The heart of the capybara was located from the second intercostal space to the sixth rib. The frenicopericardial ligament attached the fibrous pericardium to the sternum and the diaphragm. The intervenous tubercle was poorly developed. In the right atrium, there were few pectinated muscles. The right papillary muscles had septomarginal trabeculae among them. The carnous trabeculae showed a marked development on the marginal wall of the right ventricle. There were also large, carnous trabeculae on the septal wall, which was somewhat flatter. The left papillary muscles were two, located opposite each other and on the septal wall. Both were simple and sent tendinous cords to both cusps of the left atrioventricular valve. Carnous trabeculae of the left ventricle were less numerous. Between both papillary muscles there was a large carnous trabecula that occupied much of the dorsoventral extension of the septal wall of the left ventricle. Of both coronary arteries, the left coronary artery that emerged from the left coronary sinus of the aorta was the most important, with larger size and greater distribution. The paraconal interventricular branch was directed through the paraconal interventricular groove and terminated on the right ventricular margin anastomosing with the subsinusal interventricular branch that came through the groove of the same name. With other techniques, it is necessary to perform histological, semiological and physiological studies in the heart of this species to better understand its anatomy and physiology.
KEY WORDS: Circulatory organs; Coronary arteries; Rodentia; Cardiovascular system.