Background: Acute treatment strategy and subsequently prognosis are influenced by the duration of ischemia in patients with ST-elevation acute myocardial infarction (AMI). However, timing of ischemia may be difficult to access by patient history (historical timing) alone. We hypothesized that an electrocardiographic acuteness score is better than historical timing for predicting myocardial salvage and prognosis in patients with anterior AMI treated with fibrinolysis or primary percutaneous coronary intervention. Methods: One hundred seventy-five patients with anterior infarct without electrocardiogram (ECG) confounding factors were included. The ECG method for estimating timing of AMI was calculated using core laboratory measurements from the initial 12-lead ECG. Historical timing was recorded as time from symptom onset to initiation of reperfusion therapy. Myocardial salvage was determined by ECG, using the Aldrich score to determine the initially predicted myocardial infarct size and the Selvester score to determine the final QRS-estimated myocardial infarct size. Results: The mean amount of myocardium salvage depended on ECG timing (43% [±38%] for "early" vs 1% [±56%] for "late"; P < .001), whereas myocardial salvage was independent of historical timing (P = .9). One-year mortality was predicted from ECG timing (P = .04). Conclusions: The ECG method of timing was superior to historical timing in predicting myocardial salvage and prognosis after reperfusion therapy. This study suggests that ECG estimated duration of ischemia might provide a better and objective means to select acute reperfusion therapy rather than the subjective patient history, which could preclude proper reperfusion in some patients with salvageable myocardium.