The foramen ovale is an opening in the part of the heart that separates the upper right and left chambers (atria). In a fetus, this opening allows blood to flow to the left side of the heart without going to the lungs, and it is kept open by the pressure of the blood that passes through it.

Normally, when the baby is born and takes his or her first breath, blood begins to flow through the lungs, and the foramen ovale closes within a few days. A foramen ovale that remains open beyond that time is considered a heart defect (patent foramen ovale). Treatment for an open (patent) foramen ovale includes surgical repair.