How your Heart Works

The healthy heart weighs well under a pound and is only a little larger than your fist. It is a powerful, continuously hard-working organ. In addition to maintaining a steady, normal flow of blood it must be able to adjust and adapt quickly to the body's ever changing needs. For example, it must pump more blood with strenuous activity and less blood when you are at rest. In an average day, the heart will contract an average of 60 to 90 times per minute - 42 million heartbeats per year! Your heart is actually a two-sided pump responsible for circulating blood throughout your body. Inside your heart there are four chambers. A wall of muscle called the septum divides your heart into a left side and a right side.

Each side has two chambers. The upper chambers are called atria, and the lower chambers are the ventricles. The right atrium receives all the returning blood from the upper and lower part of the body. It then transfers this blood through the tricuspid valve to the right ventricle, which then pumps the blood through the pulmonary valve out to the lungs. In the lungs, carbon dioxide is exchanged for oxygen, then the blood returns to the left atrium, which transfers it through the mitral valve into the left ventricle. The left ventricle then pumps the blood through the aortic valve out to the body through the arteries where the blood supplies tissues with oxygen and removes carbon dioxide. The blood, now depleted of oxygen, is returned to the right atrium by the veins.