Blood from the systemic circulation of the body is returned to the right atrium of the heart by the large veins called the superior and inferior vena cava. Deoxygenated blood used by heart tissue itself is returned to the right atrium by a coronary vein termed the coronary sulcus, and a number of smaller coronary veins that also return blood directly to the right atrium.

The inferior vena cava, which runs through the thorax, returns blood from the abdomen, legs, and hepatic circulation (the hepatic portal system of the liver) runs along the frontal (anterior) side of the spine and lies next to the abdominal aorta (a continuation of the thoracic aorta). After passing through the diaphragm that separates the thoracic from the abdominal cavity, the inferior vena cava continues onward to the heart for approximately 1 in. (2.5 cm) before it fuses with, and empties its contents...