The cardiovascular system of tunas, as in many fish species, can be described in terms of two RC networks, in which the system is supplied by a single generator (the heart). The ventral and dorsal aorta feed resistance of the gills and systemic vasculature, respectively. The heart in tunas is contained inside a fluid-filled pericardial cavity. Their hearts are exceptionally large, with ventricle masses and cardiac output roughly four to five times larger than those of other active fishes. They consist of four chambers, as in other teleosts: sinus venosus, atrium, ventricle, and bulbus arteriosus.