1. From the Cardiovascular Branch (A.N.R., P.V.K., C.O., R.D., R.J.A., V.J.W., W.H.S., O.K., A.J.D., V.K.R., R.J.L.) and the Laboratory of Cardiac Energetics (M.A.G., S.S., E.R.M.), Division of Intramural Research, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Md; Cardiovascular Section, Department of Medicine, University of Wisconsin, Madison (A.N.R.); and Department of Radiology, The Johns Hopkins University, Baltimore, Md (P.V.K., M.X., E.A.).