Background ¹⁸F-fluorodeoxyglucose (FDG) positron-emission tomography (PET) is assumed to be the most useful method of evaluating the viability of the myocardium, but its use is limited by the need for a cyclotron. In the present study, the ability of a combination of ^99mTc-tetrofosmin (TF) and ¹²³I-β-methyliodophenyl pentadecanoic acid (BMIPP) single-photon emission computed tomography (SPECT), a combination of ¹⁸F-FDG PET and ¹²³I-BMIPP SPECT, and a combination of ¹⁸F-FDG PET and ^99mTc-TF SPECT were compared to predict functional improvement of ischemic myocardium after a large acute myocardial infarction (AMI). Methods and Results Ten patients with large AMI were studied by ^99mTc-TF SPECT, ¹²³I-BMIPP SPECT and ¹⁸F-FDG PET within 3 weeks. Six months later, ^99mTc-TF imaging was performed. All patients underwent successful revascularization, and had no restenosis. Regional tracer uptake was scored using a 4-point scale in 20 segments of the SPECT and PET images. When the defect score of ¹²³I-BMIPP SPECT exceeded the defect score of ^99mTc-TF SPECT or ¹⁸F-FDG PET by 1 point or more, and when the defect score of ^99mTc-TF SPECT exceeded the defect score of ¹⁸F-FDG PET by 1 point or more, the segment was considered to show mismatching. When the defect score was the same in 2 tracers, the segment was considered to show matching. ^99mTc-TF imaging at 3 weeks and 6 months used quantitative gated SPECT (QGS) to score wall motion using a 6-point scale (-1= dyskinesis, 0= akinesis, 1= severe hypokinesis, 2= moderate hypokinesis, 3= mild hypokinesis, and 4= normokinesis). The sensitivity of the combination of ¹²³I-BMIPP and ^99mTc-TF imaging in predicting functional improvement was 61%, that of ¹⁸F-FDG PET and ¹²³I-BMIPP SPECT was 94%, and that of ¹⁸F-FDG PET and ^99mTc-TF SPECT was 76%. The specificity of the combination of ¹²³I-BMIPP and ^99mTc-TF imaging in predicting functional improvement was 83%, that of ¹⁸F-FDG PET and ¹²³I-BMIPP SPECT was 40%, and that of ¹⁸F-FDG PET and ^99mTc-TF SPECT was 49%. The accuracy of the combination of ¹²³I-BMIPP and ^99mTc-TF imaging in predicting functional improvement was 70%, that of ¹⁸F-FDG PET and ¹²³I-BMIPP SPECT was 71%, and that of ¹⁸F-FDG PET and ^99mTc-TF SPECT was 63%. Conclusion The combination of ¹²³I-BMIPP and ^99mTc-TF imaging is a practical modality for predicting the functional improvement of ischemic myocardium after a large AMI. (Circ J 2005; 69: 311 - 319)