Over a lifetime, the heart works ceaselessly pumping blood to the lungs and throughout the body. This hollow, muscular organ contains four chambers. The lower right chamber -- the right ventricle -- receives deoxygenated blood from the body. This blood is pumped to the right atrium where it flows out of the heart to the pulmonary artery that carries it to the lungs. In the lungs, oxygen is added to the blood and carbon dioxide is removed through exhalation. The oxygenated blood enters the left atrium through the pulmonary veins and is passed to the left ventricle where it is pumped to the entire body. This interaction between heart and lungs delivers oxygen and nutrients to all the cells in the body, while carbon dioxide and other wastes are carried away to be removed by the lungs, liver and kidneys.