A 50-year-old woman who had atrial septal defect surgery at 11 months old underwent ascending aortic aneurysm resection and two attempts at closure of a residual atrial septal defect. Post-operatively, she had severe cyanosis. She was referred to our centre where a transesophageal echocardiogram and cardiac catheterisation showed an iatrogenic interatrial tunnel-type communication that was closed with an Amplatzer Vascular Plug.