Patent foramen ovale

Atrial septal defect (ASD) is a congenital heart defect in which blood flows between the atria (upper chambers) of the heart. Some flow is a normal condition both pre-birth and immediately post-birth via the foramen ovale; however, when this does not naturally close after birth it is referred to as a patent (open) foramen ovale (PFO). [Source: Wikipedia ]

OrphaNet reference
Patent foramen ovale 
May Cause
Right atrial enlargement