Carbon-11 acetate positron emission tomography (PET) has been widely used to assess regional oxidative metabolism of the heart. However, the accuracy of [11C]acetate PET in assessing oxidative metabolism in infarcted myocardium remains controversial. Thirteen patients with stable coronary artery disease and old myocardial infarction were studied. The 15O-based PET studies yielded regional blood flow (rMBF, ml/min/g) and oxygen consumption (rMMRO2, ml/min/g), which was compared with the myocardial clearance rate constant (kmono) of [11C]acetate in segments with rMBF > or = 75% (group A), 50%-74% (group B) or < 50% (group C) of the normal reference segment. Mean MBF was 0.96 +/- 0.08 ml/g/min in group A, 0.67 +/- 0.06 ml/g/min in group B and 0.42 +/- 0.07 ml/g/min in group C segments. The segmental rMMRO2 correlated linearly with kmono (r = 0.89, P < 0.001, y = 0.61x + 0.026). The kmono/rMMRO2 ratio was comparable in the group A and B segments (0.99 +/- 0.19 vs 1.07 +/- 0.21, P = NS). However, the ratio was significantly higher in the group C segments (1.28 +/- 0.35, P = 0.037). It is concluded that kmono of [11C]acetate correlates linearly with rMMRO2 determined by [15O]O2 inhalation. However, kmono appears to yield higher rMMRO2 estimates than the [15O]O2 method in low-flow areas.