Objective: The aim of the study was to determine IRA (infarct-related artery) by analysis of the initial ECG (electrocardiogram) in patients with acute inferior wall myocardial infarction. Methods: Fourty patients (36 male, 4 female) admitted to coronary care unit with the diagnosis of acute inferior wall myocardial infarction were included in the study. The mean age of patients was 62.2 year (29-85 years). The coronary angiography was performed in all patients at the first week of admission. To determine the relationship between IRA and R/S ratio, ST segment depression in lead aVL, statistical analysis was performed. Results: IRA was the right coronary artery (RCA) in 20 cases, circumflex artery (Cx) in 15 cases, RCA+Cx in 5 cases. R/S ratio was bigger than one in patients with Cx lesion and R/S ratio was smaller than one in patients with RCA lesion. The degree of the ST segment depression was equal or smaller than 2 mm in patients with Cx lesion and greater than 2 mm in patients with RCA lesion (p<0.05). There was no correlation between IRA and precordial reciprocal electrocardiographic changes. Diagnosis of right ventricular infarction was established in 75% of patients with RCA lesion, 26% of patients with Cx lesion and 100% of patients with RCA+Cx lesions. Conclusion: We concluded that it was possible to predict IRA after examining the initial ECG changes such as R/S ratio, ST segment depression. This prediction can shorten the time required to perform primary percutaneous transluminal coronary angioplasty. Non-invasive prediction of IRA was useful for suggestion of clinical course in patients with high complication risk, such as patients with RCA lesion