The heart is a powerful muscle with the specific job of pumping blood around the body. It is divided into 4 hollow areas called chambers that work together as two parallel pumps. The four chambers include two atria and two ventricles. The right atrium and right ventricle make up one pump that propels blood through the pulmonary circulation to the lungs. The left atrium and left ventricle compose the second pump that propels blood through the systemic circulation to all other tissues of the body.

The heart works in two cycles. Its continuous pumping action keeps the body supplied with oxygen-rich blood. The cells of the body take the oxygen they need from the circulating blood. In the first part of the cycle the blood returns to the right side of the heart, which pumps the blood into the lungs to pick up oxygen. The oxygen-rich blood then enters the left side of the heart where it is pumped out to circulate throughout the body.
The heart beats approximately 60-100 times each minute and pumps about 3-5 liters of blood every minute.