Contractions of the left ventricle pump the blood through the aortic valve into the aorta.

In the capillary bed, oxygen and nutrients leave the blood and enter cells while carbon dioxide and metabolic waste products leave the cells and enter the bloodstream.

The capillaries connect arterioles to tiny venules, which empty into small veins that carry blood into larger veins and, eventually, the inferior and superior vena cavae.

The systemic circulation -the distribution of oxygenated blood to the body’s tissues and the return of deoxygenated blood to the heart- begins at the left side of the heart.

From the left atrium, oxygenated blood passes through the mitral valve and enters the left ventricle.

Four valves control the flow through the atria and ventricles and into the pulmonary and systemic circulations.

Heart valves are named for their appearance and location.One way to remember the function of arteries is that Arteries carry blood Away from the heart; the only exception are coronary arteries, which is explained below.When the left atrium fills with oxygenated blood from the lungs, it contracts and forces blood through the mitral valve into the left ventricle.Thus, the coronaries fill during diastole when the ventricles are relaxed and the aortic-valve leaflets have snapped back down.During ventricular systole, the valves between the atria and the ventricles (the tricuspid and mitral) are closed, so that blood may be ejected forward into the blood vessels.Diastole is the period of relaxation during which the ventricles or atria fill with blood.