1. From the Departments of Cardiology (N.D.B., S.B.P., J.F.K., S.A.N.G., J.E.L.), Radiology (V.M.), and Cardiovascular Surgery (J.E.M., R.A.J., A.R.C.), Children's Hospital; and the Departments of Pediatrics (N.D.B., S.B.P., J.F.K., S.A.N.G., J.E.L.), Radiology (V.M.), and Surgery (J.E.M., R.A.J., A.R.C.), Harvard Medical School; both in Boston. Address reprint requests to Dr. Lock at the Cardiology Department, Children's Hospital, 300 Longwood Ave., Boston, MA 02115.