Abstract Areas of myocardial infarction may retain grycolytic activity and this finding is indicative of tissue viability and predictive of functional recovery after revascularization. In order to assess the relation between the time elapsed from the occurrence of acute myocardial infarction and persistence of myocardial metabolic activity in the infarcted tissue, we prospectively studied 65 patients with previous myocadrial infarction diagnosed clinically and by etectrocardiographic (Q wave) and enzymatic criteria. All patients underwent coronary angtography and contrast left ventriculography, evaluation of regional myocardial glucose metabolism (in the fasting state) by positron emission tomography (PET) with 2-[ 18F]fluoro-2-deoxy- d-glucose ([ 18F]FDG), and assessment of myocardial perfusion by single photon emission computed tomography (SPECT) with technetium-99m methoxyisobutyl isonitrlie ( 99mTc-MIBI). Based on the regional metabolic and perfusion findings, patients were divided into 2 groups, depending on the absence (group 1, 26 patients) or presence (group 2, 39 patients) of [ 18F]FDG uptake in the underperfused regions. Areas of underperfusion at rest, consistent with the clinically identified myocardial infarction site, were observed in all patients. Severity of coronary artery disease, presence of collaterals, number of hypocontractile segments, and wall motion score did not differ significantly in the 2 groups. The time elapsed from the infarction was significantly greater (1,860 ± 1,333 days) in group 1 than in group 2 (92 ± 115 days; p < 0.0001). Exercise caused an increase in severity and/or extent of resting perfusion abnormalities in a greater proportion of patients of group 1 (53% vs 23%). A higher prevalence of exercise-induced ST-segment elevation was observed in group 2. Thus, our study demonstrates that the majority of recently infarcted myocardial regions retain residual metabolic activity, the extent of which is inversely related to the time elapsed from the occurrence of the acute event. This may suggest that the myocardium that has survived the initial ischemic insult, but remains severely underperfused for prolonged periods of time, may eventually succumb to necrosis and be replaced by scar tissue. However, the possibility that PET scanning using [ 18F]FDG to assess myocardial metabolism may trace only postischemic stunned myocardium, has also to be considered.