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 has a flap of tissue that acts like a one-way door—it 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. Sometimes, this opening remains open (patent) and is called a patent foramen ovale. A patent foramen ovale is also called a PFO. A PFO happens in about 2 out of 10 people.

A patent foramen ovale is typically not treated and does not cause problems. But it might be treated if other heart defects are present or you had a stroke caused by a blood clot. Treatment includes a catheter procedure or surgery to close the opening in the heart.