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). Patients with a small or moderate ASD or with a PFO are asymptomatic unless a complication occurs.Generally an ASD hole is larger than a PFO. The larger the hole, the more likely symptoms are. 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. 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. A PFO is similar in location to atrial septal defect (ASD), but it is smaller and rarely causes problems on its own. Patients with a small or moderate ASD or with a PFO are asymptomatic unless a complication occurs.