Abstract In this era of thrombolytic therapy, the standard 12-lead electrocardiogram (ECG) is easily available and noninvasive and could provide indictors of myocardial reperfusion and salvage. Previous reports have proposed that a decrease of total ST-segment elevation of ≥20% from the pre- to the immediate posttreatment ECG is indicative of reperfusion, and that a ≥20% decrease from the initial infarct size predicted by ST-segment deviation on the admission ECG to the final infarct size estimated by QRS score on the predischarge recording is indicative of myocardial salvage. This prospective study of 29 patients with myocardial infarction and angiographically documented reperfusion shows that the ≥20% threshold for ST resolution achieved 79% sensitivity and 70% specificity in patients receiving intravenous therapy and 90% sensitivity in those receiving rescue intracoronary therapy. However, it should be noted that 21% of patients with successful intravenous therapy failed to achieve even this threshold of ST resolution. Regarding myocardial salvage, 63% of patients receiving intravenous and 90% of those receiving rescue intracoronary therapy achieved the threshold of ≥20% decrease in infarct size.