The heart has two sides (a right and a left) and is comprised of four chambers (see fig. 1). The two atria, right and left, receive blood from the body and lungs. The atria pump blood to the two ventricles. The ventricles are the two lower chambers of the heart (see fig. 2). They have thick muscular walls. The right ventricle receives deoxygenated blood from the right atrium and pumps blood through the pulmonary artery to the lungs. The left ventricle receives oxygenated blood from the left atrium and pumps it through the aorta, which carries it to the rest of the body.

Figure 1: Cut away view of the heart from the front.

Figure 2: Ventricles of the heart.