Background: Myocardial infarction (MI) is a high-risk condition especially when filling pressure is raised, and earlier reports have suggested that E/e' is associated with poor outcome. However, whether E/e' predicts risk better than LVEF, which is the current standard of practice, is not known. We investigated this question in the largest and most rigorous study of MI patients so far. Methods and Results:We studied 660 patients with ST-elevation MI (STEMI) treated with primary percutaneous coronary intervention and related E/e' to short-term mortality (in-hospital death), as well as long-term events at 2 years comprising (a) a composite of MI, stroke, heart failure, and death, and (b) death alone. Short-term models were adjusted for age, sex, and LVEF. Long-term models were adjusted for age, sex, diabetes, revascularization procedure, history of MI, hypertension, renal function, drugs on discharge, and LVEF. Elevated E/e'> 15 indicated higher risk of short-term events (n = 19:7.0% (95% confidence interval 3.4-10.8%) vs. 1.0% (0.3 -2.3%); adjusted odds ratio 3.7 (1.3-10.5)). While elevated E/e' was also associated with long-term outcomes (n = 103 composite events: 15.9% (11.9% -21.4%) vs 6.8% (5.2% -8.7%), P < .001; n = 38 death events: 6.0% (3.9% -9.5%) vs 2.0% (1.3% -3.2%), P = .001), E/e' was rendered nonsignificant for long-term outcomes by multivariable adjustment (p = ns for both). LVEF, on the contrary, was a highly significant predictor in the adjusted long-term model. Conclusion:E/e' is associated with poor outcome in STEMI, but LVEF is a stronger predictor of long-term risk. K E Y W O R D S E/e', echocardiography, filling pressure, myocardial infarction S U PP O RTI N G I N FO R M ATI O N Additional supporting information may be found online in the Supporting Information section.