Prior studies have proposed several electrocardiogram criteria for identifying patients with acute inferior ST-segment elevation myocardial infarction (iSTEMI) caused by obstruction of the proximal part of the right coronary artery (RCA). We applied 11 of these criteria and three new ones to the admission electrocardiograms of 80 patients admitted with an acute iSTEMI in order to evaluate their utility. All patients received thrombolytic treatment and underwent coronary angiography during the hospitalization. Four previously described criteria (ST-segment depression in lead V1, ST-segment depression in leads V1-V3, maximum ST-segment depression in the precordial leads, and ST-segment depression in lead V3 of <or= 50% of the magnitude of ST-segment elevation in lead III) and two new used criteria (the absence of ST-segment depression in lead V1 in combination with ST-segment depression in lead V2 and the arithmetic sum of the ST-segment: III + V3 > 1) were useful in identifying patients with obstruction of the proximal part of the RCA. Among the six criteria, ST depression in V1-V3 had the highest specificity (77.2%) and positive predictive value (56.5%), and a new criterion-the arithmetic sum of the ST-elevation in V3/ST-elevation in III < 0.5--had the highest sensitivity (80.9%) and negative predictive value (86.7%). Six criteria were helpful in identifying patients with acute iSTEMI caused by obstruction of the proximal part of the RCA. One of these has not been previously reported and has the higher specificity and negative predictive value.