PFO (Patent Foramen Ovale) and ASD (Atrial Septal Defect) are congenital heart conditions that affect the structure of the heart. 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. 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). Generally an ASD hole is larger than a PFO. The larger the hole, the more likely symptoms are. Learn more about the causes and complications of this condition in which a hole in the heart doesn't close the way it should after birth. Patent foramen ovale (PFO) and atrial septal defects (ASDs) represent the most common and second most common congenital heart abnormalities.