Heart: What exactly do these do?

The right atrium receives de-oxygenated blood returning from systemic circulation via the superior and inferior vena cavae. The right ventricle pumps the de-oxygenated blood through the pulmonary artery to the lungs, where it picks up oxygen from alveolar surfaces. The oxygenated blood is returned to the left atrium via the pulmonary vein, and the left ventricle contracts, pushing it out of the heart through the aorta, where is travels throughout the body, supplying oxygen to organs and muscles.