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. 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. 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. An atrial septal defect (or ASD) is a hole in the wall (septum) that divides the left and right collecting chambers of the heart (atria). Patent foramen ovale (PFO) and atrial septal defect (ASD) are holes in the wall that separates the two upper chambers of your heart.