There are two types of holes which can be present between the upper chambers of the heart: an Atrial septal defect (ASD) and a patent foramen ovale (PFO). ASD is a birth defect with a gap in the heart's upper wall.This gap happens when the wall does not form right before birth. A review of atrial septal closure, including the surgical evolution and the subsequent progression of transcatheter device closure. Generally an ASD hole is larger than a PFO. The larger the hole, the more likely symptoms are. In this case, elevation of pressure in the pulmonary circulation (e.g. Patent foramen ovale (PFO) and atrial septal defect (ASD) are holes in the wall that separates the two upper chambers of your heart. They can range from a small opening, a series of holes, or the complete absence of the atrial septum. A pfo is a type of an asd.