Heart, artwork. The heart is a hollow muscle that pumps blood around the body. The vena cava (down left) returns deoxygenated blood from the body to the heart's right atrium (chamber, upper left). The blood flows into the right ventricle (chamber, centre), which contracts to push the blood through the pulmonary artery (upper centre) to the lungs. The tricuspid valve (blue with strings at left) prevents the backflow of blood during the contraction. From the lungs, newly oxygenated blood enters the left atrium (orange, upper right) and flows to the left ventricle. The left ventricle contracts to push the blood to the aorta (arched) and around the body. The mitral valve (blue with strings at right) prevents backflow to the left atrium. The pulmonary valve (blue circular, upper centre) and the aortic valve (blue ciruclar, centre right) prevent backflow into the venrticles.