Unusual interatrial fistula discovered during device closure of an atrial septal defect.

Atrial septal defect (ASD) closure is a common reason for referral to the cardiac catheterization laboratory. We report a case in which a relatively large Qp:Qs of 1.85:1 was demonstrated in the face of a small secundum ASD. This led to further investigation, ultimately leading to the discovery of an unusual atrial fistula. Rare cases of interatrial tunnels have been described in the literature, however, this is a unique case of a left atrial appendage to right atrial appendage fistula in the setting of a right juxtaposed left atrial appendage.