This 3D medical animation shows how deoxygenated blood flows out through the pulmonary arteries into the lungs and out to the small peripheral vessels. Oxygenated blood returns from the pulmonary veins back into the left atrium of the heart, from the atrium into the left ventricle and then out of the heart through the aorta. Blood pumped out into the aorta enters into the coronary arteries to flow across the surface of the heart providing oxygen to the heart muscle.