While the QRS scoring system has been established as a convenient tool for estimating infarct size in nonreperfused patients during the chronic stage of myocardial infarction, its applicability to reperfused patients in the acute stage has not been established. To investigate whether infarct size could be estimated by the QRS scoring system soon after reperfusion, we evaluated QRS scores obtained serially 6 hours to 1 month after reperfusion, total creatine kinase release, and left ventricular ejection fraction in 126 patients with acute myocardial infarction who underwent successful reperfusion therapy. A significant correlation was observed between the QRS score obtained after 6 hours and that obtained after 1 month ( r = .89). The QRS scores obtained after 6 hours and 1 month were significantly correlated with total creatine kinase release ( r = −.65 and r = −.75, respectively) and left ventricular ejection fraction ( r = .62 and r = .76, respectively). Thus, the QRS scoring system can be used as a simple and economical method for estimation of infarct size soon after reperfusion.