Circulation Journal Official Journal of the Japanese Circulation Society http://www. j-circ.or.jp he energy metabolism of the heart and the utilization of substrates including glucose, fatty acids, amino acids, lactic acid and ketone bodies depend on circumstances, 1 and are primarily based on fatty acid metabolism and glucose metabolism in a competitive manner. 2 However, a shift to anaerobic metabolism because of low oxygen supplies causes ischemic myocardium to primarily utilize glucose. 3,4 Many reports have discussed whether maintaining glucose metabolism is important in estimating the viability of ischemic myocardium, and some reports indicate that improvements in left ventricular function and the prevention of cardiac events are achieved with the use of aggressive revascularization procedures. 5-9 The use of glucose-loaded 18 F-fluoro-2-deoxyglucose ( 18 F-FDG) PET has played a central role in helping cardiovascular interventionalists decide whether revascularization procedures are indicated in patients with old myocardial infarction (MI) with residual stenosis and angina pectoris. 10-13 18 F-FDG-PET has been also utilized to evaluate systemic inflammatory diseases, including malignancies, because 18 F-FDG accumulates in sites of inflammation. 14,15 Therefore, appropriate timing for the evaluation of glucose-loaded 18 F-FDG-PET images of acute MI (AMI) has been conventionally considered T