Your heart is a beautifully designed pump whose purpose is to deliver blood, together with life-giving oxygen and nutrients, to every cell, tissue, and organ of your body. Shaped like a pear and weighing about eleven ounces, the heart sits in the center of the chest, pointing up toward the right shoulder. It is a specialized muscle divided into four chambers, two on the right and two on the left, which are separated by one-way valves. The heart therefore is in a sense two pumps, because it's right and left sides are separated from each other.

There are four chambers in the heart, two--an atrium and a ventricle--on either side. The right atrium is a receptacle for the veins transporting blood back into the heart. When it has filled, the chamber's muscle contracts and empties its contents through the tricuspid valve and into the right ventricle.

The right ventricle transports oxygen-depleted blood to the lungs across the pulmonary valve and into the pulmonary artery and its branches. The blood travels into progressively smaller arteries and eventually into tiny vessels called capillaries. These vessels have very thin and delicate linings that allow oxygen and other nutrients to move into and out of the bloodstream. The oxygen in the lungs moves across the capillary membranes and into the blood, where it hooks up with the red blood cells. The capillaries also eliminate carbon dioxide, received from the tissues and cells of the body, to the lungs where it is exhaled into the atmosphere.

Once these exchanges have been completed, the blood moves through the pulmonary vessels to the left side of the heart. The left atrium is the collecting chamber. Once it is full, the left atrium moves its contents across the mitral valve into the left ventricle.

The left ventricle is by far the most powerful pumping chamber of the heart. Its contents must be propelled under pressure much higher than in the other chambers, so the oxygen-enriched blood can travel through the arteries of the body at a sufficient pressure to reach every cell and organ. Its powerful thrust sends blood through the aortic valve and into the aorta, the largest artery in the body. From there the blood continues flowing to the arteries.

This extraordinary round-trip takes about a minute and repeats itself every minute of your life. In an average person's lifetime, it is estimated that the heart contracts 2.5 billion times! Each day, the average heart beats some 100,000 times and pumps more than 2,000 gallons of blood through the equivalent of approximately 60,000 miles of blood vessels! Your heart is a mighty organ indeed!