BACKGROUND In patients with acute myocardial infarction (AMI), QRS score at presentation electrocardiogram (ECG) may reflect the evolutionary stage of the infarction and allow one to predict the degree of myocardial reperfusion potentially achievable by reperfusion therapy. RESULTS The relationship between QRS score on admission ECG and myocardial blush grade, an angiographic marker of myocardial reperfusion, was examined in 416 patients with a first anterior AMI who received reperfusion therapy within 6h after symptom onset. Patients were classified into 3 groups according to QRS score: 0 or 1 (n=102), 2-4 (n=228), and ≥5 (n=86). Higher QRS scores were associated with a longer time to admission, a greater ST-segment elevation, a higher frequency of impaired initial and final culprit coronary vessel flow, a higher peak creatine kinase level, and a higher frequency of impaired myocardial reperfusion as defined by myocardial blush grade 0/1 on the final angiogram. Multivariate analysis showed that a high QRS score ≥5 was the strongest predictor of impaired myocardial reperfusion (odds ratio 20.3, P<0.001). These findings were similar when the data were stratified according to time to admission (≤2h, >2h). CONCLUSIONS In patients with a first anterior AMI treated by reperfusion therapy, admission high QRS score ≥5 strongly predicts impaired myocardial reperfusion, even when presentation is early (≤2h).