Structure of a human heart. Computer artwork of a heart with the left atrium (first chamber) removed, showing the inside of the left ventricle (second chamber). Oxygenated blood (red) flows from the lungs through the pulmonary vein (not seen) into the left atrium of the heart. It is then pumped through the mitral valve (yellow) into the left ventricle. From here it is pumped out through the aorta (red pipe) to the body. Deoxygenated blood (blue) from the body enters the right atrium (blue, upper right) through the vena cava (blue pipe), passes into the right ventricle and is then pumped to the lungs through the pulmonary artery (not seen). The smaller blood vessels supply the heart itself.