Why do these birth defects occur? ASD is a development issue, leaving a lasting hole.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. 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. PFOs can occur only after birth when the foramen ovale fails to close.