Generally an ASD hole is larger than a PFO. The larger the hole, the more likely symptoms are.An atrial septal defect (ASD) and a patent foramen ovale (PFO) are both openings in the atrial septum. 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). An ASD closure device fixes an opening between your upper heart chambers (atria). This treats atrial septal defects (ASD) and patent foramen ovale (PFO). 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. 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.