In this way, blood returns from the body to the right side of the heart and is pumped to the lungs for gas exchange. The story on the left side of the heart is practically identical to the right, but the names change. Oxygenated blood from the lungs arrives at the left atrium from the pulmonary vein. During diastole, blood flows through the mitral valve into the left ventricle. As systole begins, intraventricular pressure rises, shutting the mitral valve and opening the aortic valve.
Blood flows out the aorta to feed the systemic circulation.
As the ventricle again begins to relax, the aortic valve snaps shut and the ventricle begins to fill. While the basic geometry and function of the two sides of the heart are very similar, they have different jobs. The right supplies blood only to the lungs, while the left must pump blood to the rest of the body. It is not surprising that the left side of the heart must develop pressures ten times higher than those on the right side. This must certainly contribute to the fact that heart valves on the left side of the heart are most often affected by disease.