Human heart. Computer-digitised, historical illustration of a healthy human heart. Main arteries that service the heart are visible, with coronary arteries branching on its ventricular surface. As a pump the heart circulates blood around the body. It consists of four chambers. Two chambers on the left side (at right on image) receive oxygenated blood from the lungs and pump it to the body via the aortic arch artery (top centre). Used blood drained from the body is collected and pumped through the right side of the heart, to the lungs via pulmonary arteries (upper centre, beneath aortic arch). Special mechanisms in the heart maintain its cardiac pump-rhythm.