How does the heart work
The heart is a fist sized muscular organ that pumps blood around the body. It is actually two pumps that are joined together. At the top of each side of the heart is a thin-walled chamber called the atrium which receives blood that returns to the heart through the veins. Once the atrium is filled, it contracts and squeezed its blood into a much more muscular chamber called the ventricle. The ventricle contracts in turn and forces blood at high pressure along the arteries and off to the lungs or the rest of the body. A system of one way valves stops the blood from leaking back into the heart. The left side of the heart pumps blood to the lungs to collect more oxygen.