The vena cava is a large vein in the human body that carries deoxygenated blood back to the heart. There are two main types: the superior vena cava, which collects blood from the upper body, and the inferior vena cava, which gathers blood from the lower body. Both veins empty into the right atrium of the heart. The vena cava plays a crucial role in the circulatory system by ensuring that blood returns to the heart after delivering oxygen and nutrients to the body's tissues. This process is essential for maintaining proper blood circulation and overall health.