Objective: The prone position is commonly utilized to reduce false positive perfusion defects because this position overcomes the diaphragmatic inferior wall attenuation in single-photon emission computerized tomography (SPECT) studies. We investigated whether the prone position had an important advantage over the supine position in determining the severity and extent of infarct in patients with acute inferior myocardial infarction (MI). Methods: Twenty-nine male patients (mean age 61±10 years) with acute inferior MI were enrolled in the cross-sectional study. After injection of thallium-201 (201Tl) under resting conditions, redistribution SPECT imaging was twicely performed in each subject, in both the supine and prone positions, consecutively. The extent and severity scores of the perfusion defects were calculated from the sum of individual segment scores. Myocardial infarction size was also evaluated using peak cardiac troponin T (cTnT) levels. Wilcoxon rank and Spearman’s rank correlation tests were used for statistical analyses of data. Results: For the supine vs. prone positions, the median defect severity scores were 8 (4-13) vs. 5 (0.5-8.5) and the defect extent scores were 4 (3-5.5) vs. 3 (0.5-4.5), respectively. Both perfusion defect scores in the prone position were significantly lower than those in the supine position (p<0.001). The mean peak cTnT level during hospitalization was 7.2±3.9 μg/l. Peak cTnT levels were correlated with all SPECT parameters. However, the correlation was greater in the prone position (defect severity: r=0.712, p<0.001) (defect extent: r=0.790, p<0.001) than in the supine position (defect severity: r=0.495, p<0.01) (defect extent: r=0.481, p<0.01). Conclusion: In patients with inferior MI, the SPECT results revealed a significant difference between the supine and prone images. The perfusion extent and severity scores of SPECT in the inferior wall with prone imaging correlates better with the peak troponin compared to the supine position. Comparative studies that use advanced imaging tools are needed to verify our present findings.