Cardiac metabolism in working hearts . Myocardial O2 Consumption (A) and Lactate Ratio (B) upon perfusion of 4 and 21°C cardioplegia hearts. MVO2 and Lactate ratios were determined from the differences in the respective parameters in the outflow and inflow perfusate samples. Baseline = 60 min after reperfusion, at hemodynamic steady state; 90 min = at peak performance. Each bar represents mean ± SEM of n = 5 for each group.