OBJECTIVE To investigate whether the ST changes in the aVR lead on 12-lead ECG can be used to identify infarct-related artery (IRA) in patients with acute inferior myocardial infarction. METHODS The ECG features were studied in 90 patients with acute inferior myocardial infarction where IRA was confirmed by coronary angiography. RESULTS Right coronary artery (RCA) and the left circumflex coronary artery (LCX) were identified as IRA in 70 and 20 patients, respectively. ST depression in aVR > or = 0.1 mV was found in 14 (70%) patients who had LCX as the IRA, and in 4 (5.7%, p<0.001) patients with RCA as IRA. Using ST segment depression > or = 0.1 mV in aVR as a criterion, the sensitivity and specificity in differentiating LCX as IRA was 70.0% and 94.3%, respectively. CONCLUSIONS ST depression in aVR is common in patients with LCX-related acute inferior myocardial infarction. The ST changes in this lead are associated with an excellent specificity and a good sensitivity in differentiating LCX from RCA as the IRA.