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. Generally an ASD hole is larger than a PFO. The larger the hole, the more likely symptoms are. Note how this appearance is different from that of a patent foramen ovale. Atrial septal defect (ASD) is a congenital heart defect in which blood flows between the atria (upper chambers) of the heart. The foramen ovale is a cardiac shunt present in the embryologic phase to bypass the lungs. You may also need a cardiac closure device for a patent foramen ovale (PFO). Patent foramen ovale (PFO) and atrial septal defect (ASD) are holes in the wall that separates the two upper chambers of your heart.