BACKGROUND AND OBJECTIVES: The implication of the shape of ST elevation in the acute phase of myocardial infarction (MI) remains unclear. SUBJECTS AND METHODS: We examined the relationship between the shape of the ST elevation and infarct size in 60 patients having had a first acute anterior myocardial infarction with reperfusion within 12 hours from the onset of symptoms. A 12-lead electrocardiogram was recorded immediately before, and on the 1st day following reperfusion. RESULTS: The shapes of the ST elevation in lead V3 of the electrocardiogram on the 1st day following reperfusion were classified into 3 types : concave, straight and convex types, with 11, 20 and 29 patients in each group, respectively. The left ventricular ejection fraction was measured by echocardiography at the time of discharge (7 days after the MI), and the concave, straight and convex types were 57.0, 52.5 and 47.7% (p<0.05), respectively. However, there were no significant differences in the mean values of peak troponin I and CK-MB among the three groups. CONCLUSION: In patients with reperfused acute anterior MI, the left ventricular function was excellent in patients with the concave type, but relatively poor in those with the convex type ST elevation on the first day following reperfusion.