The impact of time to treatment on outcomes after primary percutaneous coronary intervention (PCI) is controversial, and there are few data about time to treatment and infarct size. The EMERALD trial randomly assigned 501 high-risk patients with ST-elevation myocardial infarction undergoing primary PCI to stenting with or without GuardWire (Medtronic, Santa Rosa, California) distal protection. Infarct size using sestamibi imaging at 5 to 14 days and clinical outcomes were examined by time to treatment. There were no differences in outcomes between distal protection and control patients. Shorter time to reperfusion (<2 vs 2 to 3 vs >3 to 4 vs >4 hours) was associated with smaller infarct size (2% vs 9% vs 12% vs 11%, p=0.026), trends for better myocardial blush (p=0.08), and lower 6-month mortality rates (0% vs 0% vs 2.4% vs 5.3%, p=0.06). Incremental delays in reperfusion after 2 hours had little impact on infarct size. Shorter time to reperfusion impacted on infarct size in patients with anterior infarction (0% vs 17% vs 20.5% vs 30.5%, p=0.026), but not nonanterior infarction (3% vs 7% vs 7.5% vs 10%, p=0.23, p=0.022 for interaction). In conclusion, very early reperfusion with primary PCI is associated with smaller infarct size and has a much greater impact in anterior versus nonanterior infarction. Incremental delays in reperfusion after 2 hours have less effect on infarct size. These data have implications regarding the triage of patients for primary PCI.