A powerful muscle slightly larger than a clenched fist. It is composed of four chambers, two upper (the atria) and two lower (the ventricles). It works as a pump to send oxygen-rich blood through all the parts of the body. A human heart beats an average of 100,000 times per day. In that time, it pumps more than 4,300 gallons of blood throughout the entire body.
The heart's cycle starts when oxygen-poor blood from the body flows into the right atrium. Next the blood flows through the right atrium into the right ventricle, which serves as a pump that sends the blood to the lungs. Within the lungs, the blood releases waste gases and picks up oxygen. This newly oxygen-rich blood returns from the lungs to the left atrium. Then the blood flows through the left atrium into the left ventricle. Finally, the left ventricle pumps the oxygen-rich blood to all parts of the body. The human body has about 5.6 liters (6 quarts) of blood, all of which circulates through the body three times every minute.
Medical Modeling: The Human Heart. (asileFX). NYU Heart (Hippocrates Project). MRI data.