Your heart is actually a double pump. The right side of the heart is made up of the right atrium (upper chamber) and the right ventricle (lower chamber). The right side receives blood that is low in oxygen from all the veins in the body, and then it pumps that blood through the pulmonary artery to the lungs, where it will become re-oxygenated. The left side of the heart consists of the left atrium (upper chamber) and the left ventricle (lower chamber).