What blood vessel carries blood to the heart with least oxygen?

The blood vessel that carries blood with the least oxygen to the heart is the vena cava. There are two main vena cavae: the superior vena cava, which collects deoxygenated blood from the upper body, and the inferior vena cava, which gathers blood from the lower body. Both empty into the right atrium of the heart, where the deoxygenated blood is then sent to the lungs for oxygenation.