1. From the Division of Cardiology, Department of Medicine, Stanford Cardiovascular Institute (K.S., Y.L., P.T.S., J.C.W.), Institute of Stem Cell Biology and Regenerative Medicine (K.S., Y.L., J.C.W.), Stanford University School of Medicine, CA; and Cardiovascular Research Center and Department of Physiology, Temple University School of Medicine, Philadelphia, PA (S.R.H.).