Heart. Computer artwork of a human heart, the muscular organ responsible for pumping blood around the body. Deoxygenated blood from the body enters the vena cava (upper left) and flows through the right side of the heart (far and lower left), before being transported to the lungs for oxygenation. Oxygenated blood returns from the lungs through the pulmonary veins (centre) and flows through the left side of the heart (far and lower right). It is pumped out to the body through the aorta (looped structure at upper centre). Two coronary arteries (green branches at lower left and lower right) provide the heart itself with the blood supply it needs to function effectively.