Now we move to the final and most advanced and complex cardiovascular system discussed so far- the human heart and lungs. Human hearts have four chambers, two atria and two ventricles. Deoxygenated blood in the human heart is pumped to the right atrium from the superior and inferior vena cava, where they are moved to the ventricle, which in turn pumps the blood out to the lungs through the pulmonary artery, which branches off to the left and right to distribute blood to each lung to be reoxygenated. This blood, once replenished, is transferred back to the left atrium through the pulmonary veins, then moved through the left ventricle into the aorta. The aorta, the largest blood vessel in the human body, takes this oxygen-rich blood and move it throughout the body.