The foramen ovale is an opening between the right and left atria of the fetal/infant heart. This is a pathological opening that allows blood in the infant circulation to flow from atria to atria. When blood flows in this manner it bypasses the lungs. In a vast majority of cases the foramen closes on its own shortly after the baby is born. In a small number of cases, the opening does not close on its own and these infants will have to undergo surgical repair of the foramen.
Normally the blood that leaves the right atrium enters the right ventricle. From the right ventricle the blood travels to the lungs. Infants with an open foramen ovale experience deficiencies in oxygenation because of the abnormal shunting of blood. When this occurs all tissues are deprived of oxygen.