AIMS: We studied the clinical, demographic, and angiographic factors associated with successful reperfusion and the relationship between angiographic indices and clinical outcomes in a subset of the APEX-AMI trial, which tested the efficacy of pexelizumab in ST-elevation myocardial infarction patients undergoing primary percutaneous coronary intervention (PCI). METHODS AND RESULTS: Among 5745 patients enrolled in the trial, 1018 underwent independent quantitative angiographic evaluation by a core laboratory. Successful epicardial reperfusion was defined as TIMI (thrombolysis in myocardial infarction) flow grade 3 or corrected TIMI frame count (cTFC) <28 frames, and successful myocardial reperfusion as TIMI myocardial perfusion grade (TMPG) 2 or 3. TIMI 3 flow after PCI occurred in 85%, cTFC < 28 in 58% (mean cTFC was 27 +/- 20), and TMPG 2 or 3 in 91%. Overall 90 day clinical outcomes were 2.7% for mortality and 8.2% for the composite of death, congestive heart failure (CHF), or shock. After adjustment for baseline characteristics, TMPG 2/3 after PCI was associated with younger age [odds ratio (OR) for 10 year increase 0.75, 95% confidence interval (CI) 0.59-0.96, P = 0.023], pre-PCI TIMI flow 2/3 (OR 3.5, 95% CI 1.7-7.1, P = 0.001), and ischaemic time [for every hour, OR 0.81 (0.69-0.96), P = 0.015]. TMPG 2/3 after PCI was significantly associated with 90 day mortality (adjusted hazard ratio 0.26, 95% CI 0.09-0.78, P = 0.013). Neither post-PCI TMPG nor TIMI flow grade was significantly associated with 90 day death/CHF/shock. CONCLUSION: Younger age, patent infarct-related artery at presentation, and ischaemic time predicted higher likelihood of successful myocardial perfusion, which was associated with improved survival.