A 31-year-old man (175 cm, 82 kg) was referred to the emergency department 2 h after the sudden onset of acute dyspnea. Immediate ECG showed sinus tachycardia with ST elevations from V1 through V2 and a diagnosis of septal acute myocardial infarction was made. ECG on admission to the cardiology department showed the same results plus the S1-Q3-T3 pattern. Echocardiogram revealed a normally contracting left ventricle, a distended right ventricle with free wall hypokinesia and displacement of the interventricular septum towards the left ventricle. Thrombolytic therapy with tenecteplase 8000 IU and heparin 5000 IU was administered 5-10 min after hospitalisation and the patient was haemodynamically stable 30 min later. Echocardiogram performed 12 h after thrombolysis showed a normal left ventricle and a less distended right ventricle. Lung spiral computed tomography (CT) and lower abdominal CT on the fourth day showed large emboli in the inferior pulmonary arteries of the right and left lung. Rarely, massive pulmonary embolism may mimic anteroseptal acute myocardial infarction on ECG and this case demonstrates the utility of echocardiography for a differential diagnosis, as well as the efficacy of tenecteplase for thrombolytic therapy.