1. From the Division of Cardiology, Department of Pediatrics, the Hospital for Sick Children and University of Toronto Faculty of Medicine (R.M.F.); the Department of Cardiology, the Children’s Hospital and Harvard Medical School, Boston (J.L.); and the Lillie Frank Abercrombie Section of Cardiology, Department of Pediatrics, Baylor College of Medicine and Texas Children’s Hospital, Houston, Tex (J.T.B.).