Veins are the blood vessels that carry blood to the heart. Pulmonary veins are responsible for carrying oxygenated blood from the lungs to the left atrium of the heart. Humans have four of these veins in total, two from each lung. There are two right pulmonary veins, known as the right superior and right inferior veins. These carry blood from the right lung. The fact that these veins carry oxygenated blood makes them different from all other human veins, as they are used to carry deoxygenated blood. Each pulmonary vein is linked to a network of capillaries in the alveoli of each lung. These capillaries eventually join together to form a single blood vessel from each lobe of the lung. Initially there are three vessels for the right lung, but the veins from the middle and upper lobes of the right lung tend to fuse together to form two right pulmonary veins. The right pulmonary veins pass behind the right atrium and another large blood vessel known as the superior vena cava.