As the left ventricle contracts, it pushes open the aortic valve and the blood is carried into the aorta, which distributes it to all other body organs including the heart by way of the coronary arteries. These arteries wind around the heart to keep the heart muscle supplied with oxygen and nutrients for its continuous pumping job. As wastes are produced, they are delivered through the blood to the right atrium through the vena cava. The accumulated blood pushes open the tricuspid valve, allowing the blood to pass from the right atrium to the right ventricle. After the chamber fills, the heart contracts and the pulmonary valve opens.
Blood then flows from the right ventricle into the pulmonary artery.
The pulmonary artery, which has two branches, carries blood to the right and left lungs. From the lungs, the capillary vessels carry the blood along the lungs' tiny air sacs. As the lungs breathe, carbon dioxide is passed from the body and oxygen is taken in. As this transfer occurs, the blood changes from purple or dark red to bright red. After passing through the lungs, the blood is brought by the pulmonary veins into the left atrium.