Purpose: Prior studies had proposed several Electrocardiographic (ECG) criteria for identifying the culprit artery in patients with inferior wall acute myocardial infarction (AMI), although any single criteria was not sensitive or specific enough to differentiate right from left circumflex coronary artery occlusion. The aim of this study was to elaborate an ECG algorithm enabling assignment of an occluded coronary artery in AMI. Methods: Ninety consecutive patients with inferior wall AMI were studied. The coronary angiography and percutaneous coronary intervention of the culprit lesion was performed. There were 68 with a lesion in the right coronary artery (RCA) and 22 in the left circumflex artery (LCX). Admission ECG parameters (amplitude of R-wave, ST-segment deviation) in standard 12-lead ECG plus extended (V4R to V6R) leads were subjected to classification5.0 (C5.0) analysis by clemetine12.0-SPSS. Results: C5.0 analysis assessed ST-segment deviations in lead I and amplitude of R-wave in lead V3. Assessing the ST-segment in lead I, RCA was identified as the infarct-related artery if there was ST-segment deviation ��� -1mm (ST-segment depression ��� 0.1mV) and alternatively, in cases which there was ST-segment deviation > -1mm (ST-segment depression < 0.1mV) in lead I, the letter distinction could be performed in lead V3. An amplitude of R-wave > 11mm (1.1mV) pointed to the LCX as the infarct-related artery, which were correctly classified in 77.5% and 73.3% of RCA and LCX respectively. Conclusions: By using this ECG algorithm, LCX occlusion might be distinguished early from RCA in patients with inferior AMI for appropriate reperfusion strategy.