This study determines the usefulness of electrocardiography in the emergency room for assessing the risk of cardiac rupture after acute anterior myocardial infarction (MI). The presence of ST segment elevation on the admission 12-lead electrocardiography was evaluated in 325 consecutive anterior MI patients. A forward-stepwise logistic regression analysis for cardiac rupture was performed with the covariates of age, gender, hypertension, history of MI, reperfusion therapy by coronary angioplasty, and ST segment elevations in leads I, aVL, V1-V6. Cardiac rupture occurred in 16 patients, including 7 with left ventricular free wall rupture (FWR) and 9 with ventricular septal perforation (VSP). For FWR, ST elevation in lead aVL was the only independent predictor (odds ratio = 12.1, P = .0215). For VSP, female gender (odds ratio = 5.32, P = .0201) was the independent predictor. In conclusion, in patients with acute anterior MI, ST segment elevation in lead aVL on the admission electrocardiography is a significant risk factor for left ventricular FWR.