The heart is a four-chambered muscular organ covered by a double membrane called the pericardium. It contains a right atrium and ventricle and left atrium and ventricle, separated by the tricuspid and bicuspid (mitral) valves respectively. The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs while the pulmonary veins bring oxygenated blood from the lungs to the left atrium.