Structure of a human heart. Computer artwork of a heart with the right ventricle (second chamber) removed, showing the inside of the left atrium (first chamber). Oxygenated blood (red) flows from the lungs through the pulmonary vein (red pipe, upper right) into the left atrium of the heart. It is then pumped through the mitral valve (yellow) into the left ventricle (behind). From here it is pumped out through the aorta (red pipe, upper centre) to the body. Deoxygenated blood (blue) returning from the body enters the right atrium (blue area, upper left) through the vena cava (blue pipe, upper left), 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.