Gross anatomy of the pygmy killer whale heart found in Thailand

Pygmy killer whale (Feresa attenuata) is the smallest killer whale with similar size to dolphins. This mammal lives in the deep warm sea far from the shore and avoid human. Since number of pygmy killer whales are gradually decreased and could be an endanger specie, its morphological study will be an important fundamental data for future studies and research. Heart of a male pygmy killer whale from Petchaburi province was studied anatomically and found that it was triangular-like shape with side-flatten, short, wide, with pointed apex. Subepicardial fat was not abundant. Blood supply to the heart was bilateral coronary type of supply where left coronary artery gave rise to circumflex branch and paraconal interventricular branch while right coronary artery gave rise to circumflex branch and subsinuosal interventricular branch. Paraconal and subsinuosal interventricular grooves appeared almost halfway between cranial and caudal borders of the heart and ran directly to the apex. Aortic arch gave rise 3 branches of artery. Each cranial and caudal vena cava opened to the right atrium. Both atria were large. Right auricle had smooth edge and surface while left auricle had rough edge and surface. Oval fossa, pectinate muscles, and terminal crest were found in the right atrium but intervenous tubercle was not clearly exist. Three pulmonary valves and three aortic valves were found at the origin of pulmonary trunk and aorta consecutively. Trabeculae carneae, trabeculae septomarginalis, papillary muscles, chordae tendineae, and atrioventricular valves were found in ventricles the same as other mammals. This study showed that the heart of pygmy killer whale possesses several structures similar to other mammals, but a peculiar side-flatten shape and large atria. Branching pattern of coronary arteries is the same as horse and pig while the aortic branching pattern is similar to human.