The function of human heart is to pump blood throughout the human body. Human heart has two sides - right and left. Right side always receive deoxygenated blood. While left side always receive oxygenated blood. Both the sides are divided into two chambers each. The upper two chambers are called atria while the lower two chambers are called the ventricles.

Deoxygenated blood from the right ventricle is pumped out through the pulmonary arteries into the lungs for oxygenation. After oxygenation, the blood is poured back to the heart's left atrium through the pulmonary veins.

The oxygenated blood from the left atrium passes down to the left ventricle from where it is eventually pumped out into the aorta that takes blood to various body parts through numerous arteries and arterioles. In body parts, exchange of gases takes place through a network of capillaries and finally the deoxygenated blood flows through the venules and veins. This blood finally returns back to the right atrium through the vena cavae.