Patent foramen ovale (PFO) is a hole between your heart's upper chambers. The foramen ovale is a hole in the wall between the left and right atria of every human fetus.This hole allows blood to bypass the fetal lungs. A patent foramen ovale is a small, flaplike opening in the wall between the upper chambers of the heart. However, it may cause serious complications under certain circumstances. A patent foramen ovale (PFO) is a small opening between the two upper chambers of the heart, the right and the left atrium. A patent foramen ovale (PFO) is a small hole between the two upper chambers of the heart, the right and the left atrium. Here's what you need to know. Patent foramen ovale closure is a procedure to close a hole in the heart. We use minimally invasive approaches to treat PFO without open-chest surgery.