The vena cava is either of the two very large veins into which all the circulating venous (deoxygenated) blood drains. The two vena cavae, called the superior vena cava and the inferior vena cava, deliver venous venous blood to the right atrium (one of the upper chambers of the heart) for pumping blood to the lungs. Each vena cava measures almost 2.5 centimeters in diameter. The superior vena cava collects blood from the whole of the upper trunk, head, neck, and arms. The inferior vena cava drains blood from all parts of the body below the chest.