<Tr> <Th> FMA </Th> <Td> 9240 </Td> </Tr> <Tr> <Td_colspan="2"> Anatomical terminology (edit on Wikidata) </Td> </Tr> <P> The valve of the inferior vena cava (eustachian valve) is a venous valve that lies at the junction of the inferior vena cava and right atrium . </P> <P> In fetal life, the eustachian valve helps direct the flow of oxygen - rich blood through the right atrium into the left atrium and away from the right ventricle . Before birth, the fetal circulation directs oxygen - rich blood returning from the placenta to mix with blood from the hepatic veins in the inferior vena cava . Streaming this blood across the atrial septum via the foramen ovale increases the oxygen content of blood in the left atrium . This in turn increases the oxygen concentration of blood in the left ventricle, the aorta, the coronary circulation and the circulation of the developing brain . </P>

Why is there no valve separating the right atrium from the vena cavae