Heart, illustration. The heart is a hollow muscle that pumps blood around the body. The vena cava (blue, 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, lower centre), which contracts to push the blood through the pulmonary artery (purple, upper centre) to the lungs. The tricuspid valve (white with strings at left) prevents the backflow of blood to the atrium during the contraction. The pulmonary valve (at entrance to pulmonary artery) prevents backflow into the ventricle. From the lungs, newly oxygenated blood enters the left atrium (chamber, upper right) and flows to the left ventricle (chamber, lower right). The left ventricle contracts to push the blood to the aorta (red, arched) and around the body. The mitral valve (white with strings at right) prevents backflow to the left atrium.