The heart is a huge muscular pump that is split into two parts, one on the right and one on the left. The heart’s right side is in charge of pumping deoxygenated blood to the lungs. The left side circulates oxygenated blood throughout the body. The right ventricle takes blood from the right atrium and pumps it to the lungs, where oxygen is added. The left atrium receives and pumps oxygenated blood from the lungs to the left ventricle. The strongest chamber, the left ventricle, pumps oxygen-rich blood to the rest of the body.