(A) Phosphocreatine (PCr), (B) ATP, and (C) inorganic phosphate measured by 31P NMR spectroscopy in isolated hearts perfused with mixed substrate buffer during normal workload and dobutamine challenge conditions. (D) Intracellular pH calculated from the chemical shift between PCr and Pi in isolated hearts perfused with mixed substrate buffer during normal workload and dobutamine challenge conditions. (E) Left ventricular developed pressure (LVDevP), (F) heart rate (HR), and (G) rate-pressure product (RPP), the product of LVDevP and HR, measured in isolated hearts perfused with mixed substrate buffer during normal workload and dobutamine challenge conditions. (H) Coronary flow, estimated by collecting the perfusate effluent over a 2-minute period, in Langendorff heart preparations during normal workload and dobutamine challenge conditions (n=5). Data are expressed as means ± SEM. *P<0.05 vs CON. See also Figure S2.