A 35-year-old man was referred to the emergency department after having a short syncopal episode while waiting for a Doppler scan of the lower extremities for a 4-week history of a painful right leg. He had no significant past medical history and was a non-smoker. On presentation he had severe chest pain and dyspnea associated with diaphoresis, and was hemodynamically unstable. His initial electrocardiogram (ECG) showed ST segment elevations in leads V_1-4, mimicking an anteroseptal myocardial infarction. However, the angiography showed the coronary arteries were normal and the right main pulmonary artery was partially occluded by large pulmonary emboli. The ECG changes were recorded in detail which also pointed to the diagnosis of pulmonary embolism (PE). This case shows how a PE can mimic an anteroseptal myocardial infarction on ECG, and the physiopathology of the ST elevation in PE was discussed. (Circ J 2009; 73: 1157-1159)