 The circulatory circuit sends oxygenated blood from the gills to the atrium of the systemic heart, then to its ventricle which pumps this blood to the rest of the body.Deoxygenated blood from the body goes to the branchial hearts which pump the blood across the gills to oxygenate it, and then the blood flows back to the systemic atrium for the process to begin again.Three aortae leave the systemic heart, two minor ones (the abdominal aorta and the gonadal aorta) and one major one, the dorsal aorta which services most of the body.