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). 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. Transcatheter Closure Devices. Generally an ASD hole is larger than a PFO. The larger the hole, the more likely symptoms are. This procedure is a non-surgical method of closing the tunnel in the atrial septum, using an implantable umbrella-type closure device (watchman procedure). An ASD closure device fixes an opening between your upper heart chambers (atria). This treats atrial septal defects (ASD) and patent foramen ovale (PFO). This procedure is a non-surgical method of closing the tunnel in the atrial septum, using an implantable umbrella-type closure device (watchman procedure).