1. From the Division of Cardiology, Department of Medicine (D.G.S., J.A.C.L., J.M.M., G.G., R.G.W., G.F.T., K.C.W.), Johns Hopkins Medical Institutions, Baltimore, Md; Duke Clinical Research Institute (D.G.S., G.S.W.), Durham, NC; Department of Clinical Physiology (D.G.S., H.A.), Lund University Hospital, Lund, Sweden; Memorial Hospital Research Center (R.H.S.), Long Beach, Calif; and Cedars-Sinai Heart Institute (E.M.), Los Angeles, Calif.