Patent foramen ovale repair: also called a PFO closure, is a procedure that's done to close the flap in the wall of the atrial septum. Generally an ASD hole is larger than a PFO.The larger the hole, the more likely symptoms are. A patent foramen ovale (PFO) is a hole between the heart's upper chambers (the left and right atria) that failed to close after birth. A patent foramen ovale is a small, flaplike opening in the wall between the upper chambers of the heart. Patent foramen ovale is a small flap like opening between the right atrium and left atrium in the heart. Why do these birth defects occur? ASD is a development issue, leaving a lasting hole. ASD is a defect in the septum between the heart's two upper chambers. The septum is a wall that separates the heart's left and right sides.