Opening of caudal vena cava

The opening (ostium) of the caudal vena cava is located on the caudodorsal wall of the right atrium, slightly to the right of the median plane. It enters the smooth-walled sinus venarum, caudal to the opening of the cranial vena cava and dorsal to the right atrioventricular (tricuspid) orifice.

The opening of the caudal vena cava is large and usually partially guarded by a thin, crescent-shaped valvular fold known as the valvule of caudal vena cava (valve of the caudal vena cava or Eustachian valve in humans). In dogs, this valve is variably developed and often rudimentary, but when present it directs blood flow toward the right atrioventricular orifice during atrial filling.