1. From the Department of Bioengineering (F.C.), Cardiovascular Division, Department of Medicine (K.R., E.S.Z., G.E.S., F.E.M., Y.H.), Department of Radiology (H.R., M.S., P.Y., W.R.T.W.), and Department of Surgery (J.G., R.C.G.), University of Pennsylvania, Philadelphia; and Laboratory of Cardiac Energetics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD (P.K.).