Comparative anatomical characteristics of cardiac valves in animals

Although various animals have been used as models of cardiac valvular diseases in humans, the structural characteristics of cardiac valves in animals remain unclear. In this study, we investigated cardiac valves in representative animal models for the purpose of comparative anatomy. Adult hearts from three dogs, four goats, six rabbits, and six fowls were fixed with 10% neutral-buffered formalin and analyzed gross-anatomically. Cardiac appearance was spherical or oval in dogs, goats, and rabbits, whereas it had a long conical shape in fowls. Left atrioventricular (AV) valve was composed of membranous septal and parietal cusps connected to two papillary muscles in all animals. The right AV valve was composed of membranous septal, parietal, and angular cusps with three papillary muscles in dogs and goats, membranous septal and parietal cusps attached to four papillary muscles in rabbits, and a single muscular plate without any papillary muscles and chorda tendinae in fowls. Aortic valves with thin membranous right, left, and septal semilunar cusps in dogs, goats, and rabbits had a thick membrane with a bended free border in fowls. Pulmonary valve (PV) with membranous right, left, and intermediate semilunar cusps made a large central hole by being closely attached to the surrounding wall in dogs, goats, and rabbits, whereas it protruded into half of the lumen as a thick membrane in fowls. The membranous cusp of the PV was composed of several layers in dogs and goats but was a single layer in rabbits and fowls. These findings indicate that even if animals have two completely separated atria and ventricles each, cardiac valves have species-specific morphological characteristics, especially between mammals and fowls.