OBJECTIVE To determine the incidence of early left ventricular infarct expansion within five days after first anterior ST-segment elevation myocardial infarction and the effect of early thrombolytic therapy on the incidence of early infarct expansion compared with late thrombolytic therapy. METHODS In a prospective study of 101 patients (75males and 26 females), with the first attack of acute anterior myocardial infarction, their ages ranged from 40-80 years (mean age: 61.07±10.78) who had been admitted to the Coronary Care Unit of Hawler Teaching Hospital for the period from July 2007 through to September 2009. Those who received alteplase ≤3 hours of acute myocardial infarction were labelled as group-I (49 patients) and those who received alteplase >3-12 hours were labelled as group-II (52 patients). RESULTS The incidence of early left ventricular infarct expansion was diagnosed by 2D-echocardiography and was found to be 17.8%. Group I patients had a lower incidence of early left ventricular infarct expansion (8.16%) compared with group-II (26.92%; p=0.014). Patients with early left ventricular infarct expansion had a higher frequency rate of left ventricular systolic dysfunction (94.44%) compared to patients without early left ventricular infarct expansion (8.43%; p<0.001). There was a significant difference in the incidence of in-hospital mortality between the patients who developed early left ventricular infarct expansion (11.1%) compared with patients without early left ventricular infarct expansion (1.2%; p=0.025). CONCLUSIONS Early reperfusion therapy in acute anterior myocardial infarction can decrease the incidence of early left ventricular infarct expansion, preserve left ventricular systolic function and decrease in-hospital mortality.