Patent foramen ovale is one of two types of holes in the heart. The other is called an atrial septal defect (ASD).Generally an ASD hole is larger than a PFO. The larger the hole, the more likely symptoms are. 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 known as Atrial Septal Defect, and PFO is known as Patent Foramen Ovale. Everyone is born with a small hole in the atria (upper chambers of the heart). An atrial septal defect (ASD) and a patent foramen ovale (PFO) are both openings in the atrial septum. PFO (Patent Foramen Ovale) and ASD (Atrial Septal Defect) are congenital heart conditions that affect the structure of the heart. A test called an echocardiogram is used to diagnose a PFO.