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). Why do these birth defects occur?ASD is a development issue, leaving a lasting hole. 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. Patent foramen ovale (PFO) and atrial septal defect (ASD) are holes in the wall that separates the two upper chambers of your heart. An ASD closure device fixes an opening between your upper heart chambers (atria). This treats atrial septal defects (ASD) and patent foramen ovale (PFO).