The foramen ovale is an opening or shunt in the heart tissue allowing blood to flow from the right atrium to the left atrium during fetal development. Blood oxygenated at the placenta is shunted away from the pulmonic circulation via this structure as the lungs are collapsed and not functioning and bathed in amniotic fluid. When born, the ventilatory efforts by the neonate expand the lung resulting in an acute dramatic decrease in the intrathoracic pressure and permits a greater flux of blood to perfuse the pulmonary vessels. Higher pressure in the left atrium resulting from increased pulmonary venous flow from the lungs causes the septum primum of the interatrial septum to close the opening. Over time, the tissue will seal the foramen and become the fossa ovalis.
Inability to correctly close the foramen ovale can lead to multiple conditions, ranging from a patent foramen ovale to atrial septal defects. The clinical significance varies depending mostly on the size of the opening and shunts from early congestive heart failure in the case of a significant atrial septal defect to asymptomatic in small and relatively common patent foramen ovale. Treatment options for atrial septal defects have been implemented to reconstruct the atrial septum.
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