bild

Model human heart. The heart is the hollow muscular organ responsible for pumping blood around the body. Deoxygenated blood arrives at the heart from the body through the vena cava (grey, centre). It is then pumped to the lungs to pick up oxygen through the pulmonary artery (grey, upper centre), returning rich in oxygen through the pulmonary veins. The oxygen-rich blood is pumped to the rest of the body through the aorta (red, upper centre). The heart muscle itself is supplied with blood by the coronary arteries, seen on the surface of the heart. (KEYSTONE/SCIENCE PHOTO LIBRARY/MARK THOMAS)