The main function of the heart is to pump blood to the lungs to be saturated with oxygen, and then pump it out into the body to supply the cells with oxygen. The heart, along with the blood vessels, make up the cardiovascular system.
The heart is made up of four chambers: the upper two are atria, and the lower two are ventricles. The two chambers on the right and the two on the left work together in pairs to move blood through the body. The right side moves oxygen lacking blood to the lungs to be saturated while the left side works to move the blood that is now fully loaded with oxygen back into the body. The heart also has four valves. These valves contain flaps to keep the blood from flowing the wrong direction in the heart. The two major arteries in the body bring blood to the right atrium that is lacking in oxygen. The blood then passes into the right ventricle through the valve that regulates the flow of blood between the two. Once the ventricle is full, the blood is passed into the pulmonary artery, which carries the blood to the lungs. Once the blood has oxygen once again, it returns to the left atrium to be passed into the left ventricle and into the aorta. It is then pumped into the aortic valve and into the body.