Generally an ASD hole is larger than a PFO. The larger the hole, the more likely symptoms are.ASDs frequently accompany other CHDs. 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). A patent foramen ovale is a small, flaplike opening in the wall between the upper chambers of the heart. A PFO usually closes within a few years of birth, while an ASD may remain. 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.