We studied the relationship between left ventricular oxygen consumption (LVVO2) and total ventricular mechanical energy production as determined by calculation of the systolic pressure-volume area (P-VA) before and after 25 minutes of warm ischemia in 7 sheep. We compared the relationship between LVVO2 and P-VA with the relationships between LVVO2 and stroke work and between LVVO2 and the systolic stress integral. Using the methods presented, P-VA can be measured in vivo (n = 123) in both preischemic and postischemic hearts. Ischemia increases the slopes of the relationship between LVVO2 and P-VA and between stroke work and the systolic stress integral, and reduces the oxygen utilization efficiency of stroke work to less than 2%. Coefficients of determination for the relationship between LVVO2 and P-VA are, in general, higher than those between LVVO2 and either stroke work or the systolic stress integral. We conclude that systolic P-VA can be measured in vivo using recently developed methods and that it is applicable to postischemic "stunned" hearts. Because P-VA and LVVO2 can be converted into identical energy units, calculation of P-VA permits calculation of myocardial oxygen utilization efficiency.