1. From the Division of Cardiology, Department of Medicine, Johns Hopkins Medical Institutions, Baltimore, Md (R.H.H., A.C.L., D.A.K.); Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Md (A.C.L., D.A.K.); Department of Cardiology, University of Rennes, Rennes, France (C.L.); and Laboratory of Cardiac Energetics, National Institutes of Health, Bethesda, Md (O.P.F., C.O., E.M.).