Valve of caudal vena cava

The opening of the caudal vena cava is large and usually partially guarded by a thin, crescent-shaped valvular fold known as the valve of the caudal vena cava (Eustachian valve in humans).

In dogs and other domestic animals, this valve is variably developed and often rudimentary, but when present it directs blood flow toward the right atrioventricular orifice during atrial filling.