An ASD closure device fixes an opening between your upper heart chambers (atria). This treats atrial septal defects (ASD) and patent foramen ovale (PFO).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. Generally an ASD hole is larger than a PFO. The larger the hole, the more likely symptoms are. Patent foramen ovale (PFO) is a small hole between the upper right and left chambers (atria) of your heart. This hole may let blood flow between the atria. A test called an echocardiogram is used to diagnose a PFO.