1. From the Cardiovascular Performance Program (R.B.W., A.M.H., A.L.B.) and Division of Cardiology (R.B.W., S.K.I., R.M., J.H.K., A.M.H., M.H.P., T.J.W., A.L.B.), Massachusetts General Hospital, Boston; and University Health Services, Harvard University, Cambridge, MA (F.W., B.B., A.L.B.).