The circulatory system consists of heart, veins and arteries.
The heart of turtles consists of three chambers ( the muscular ventricle is only partially divided ).
The deoxygenated blood from the venous systemis being pumped by the " fourth " chamber ( left part of the ventricle, where the hearts' beating originates ) to the right atrium, then the right site of the ventricle , where the oxygen-poor blood is prevented from mixing with the oxygenated blood by a spongy partial partition. It then enters the pulmonary artery which divides the flowing blood into two lungs where it is oxygenated.
Blood from the left atrium flows to the left side of the ventricle and then is directed to the three main arteries ( the brachiocephalic and the two aortic arches ), which direct blood to the turtles neck, head, limbs, tail and all the other vital organs.
Blood from all parts of the body, except the lungs, is returned to the heart via the sinus venosus , which recieves blood through vein systems: the precaval veins ( returning the blood from the anterior - front - part of the body ), the precaval and hepatic veins ( returning blood from the posterior - back - part of the body ), and other numerous veins.