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. Patent foramen ovale (PFO) and atrial septal defect (ASD) are holes in the wall that separates the two upper chambers of your heart. Unlike a PFO, it is a congenital defect that only some are born with. A test called an echocardiogram is used to diagnose a PFO. The test uses sound waves to create pictures of the beating heart. An ASD is a congenital heart defect, a condition that you are born with.