Generally an ASD hole is larger than a PFO. The larger the hole, the more likely symptoms are.Many people confuse ASDs with another kind of heart defect called 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. 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. A patent foramen ovale occurs when a hole that is always present in a newborn's heart fails to close as it should once the lungs begin to function after birth. Patent foramen ovale (PFO) refers to the nonclosure of the potential space between septum primum and secundum (analogous to a flap valve) 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).