Opening of inferior vena cava

The inferior vena cava, larger than the superior, returns the blood from the lower half of the body, and opens into the lowest part of the atrium, near the atrial septum, its orifice (Opening of inferior vena cava) being directed upward and backward, and guarded by a rudimentary valve, the valve of the inferior vena cava (Eustachian valve).

The blood entering the atrium through the superior vena cava is directed downward and forward, i.e., toward the atrioventricular orifice, while that entering through the inferior vena cava is directed upward and backward, toward the atrial septum. This is the normal direction of the two currents in fetal life.