9316621 Graham This study will examine heart-chamber functions in elasmobranchs (sharks and rays) and bony fishes. In fishes the heart structure consists of a single tube that is divided into four "in-series" chambers, the sinus venosus, the atrium, the ventricle, and the conus or bulbus arteriosus. In sharks, all of these, including the conus, are contractile whereas in most bony fishes, the bulbus is elastic. The cardiac chamber arrangement in fishes differs from that of mammals, including man, where there are four chambers (two atria, two ventricles) arranged in parallel. This study will examine atrial and ventricular interactions during the cardiac cycle in both sharks (hornshark) and teleost (halibut) fishes. Because of the parallel arrangement of chambers in mammals, study of chamber interaction is complicated by the actions of the four separate contractile elements that share a common central heart wall. Fishes thus offer the advantage of simpler, in-series chamber dynamics and this allows quantification of chamber-interaction effects on the volume and efficiency of the cardiac pump. Several other fish-heart features make it an important model for the mammal heart function and will be investigated in this study. Fishes have a spongy inner myocardial wall, as opposed to the smooth wall of mammals. Also, sharks differ from teleosts in having a contractile conus as opposed to an elastic bulbus. Finally, sharks lack a sympathetic cardiac innervation which parallels the condition in cardiac transplant patients. ***
