This study evaluated exercise capacity and left ventricular ejection fraction (LVEF) as predictors of long-term mortality in patients with ST-elevation myocardial infarction (STEMI) treated with percutaneous coronary intervention. LVEF is a well-established predictor of mortality in patients with STEMI. Exercise capacity, expressed as milliliters per kilogram per minutes or METs (1 MET = 3.5 ml/kg/min), may also serve as an independent predictor of mortality in this cohort. However, it is unclear whether these variables used together more accurately define mortality risk than either alone. In the Primary Angioplasty in Acute Myocardial Infarction-2 trial, 330 patients with long-term mortality data underwent radionuclide ventriculography at rest and cycle ergometer stress testing 6 weeks after percutaneous coronary intervention for STEMI. We used this database to evaluate the ability of LVEF at rest and exercise capacity to predict 2- and 5-year mortality. Exercise capacity <4 METs was a significant predictor of 5-year mortality (odds ratio [OR] 4.54, p = 0.0016). In contrast, decreased LVEF demonstrated a trend toward higher mortality but was not statistically significant at 2- (OR 2.22, p = 0.22) or 5-year (OR 2.04, p = 0.20) follow-up. When evaluated in combination, there was a statistically significant 2-year mortality risk for those with a decreased LVEF and decreased exercise capacity (OR 6.03, p = 0.018). Exercise capacity was a better predictor of 2- and 5-year mortality than LVEF in patients with STEMI treated with percutaneous intervention. In conclusion, when combined with LVEF, exercise capacity provides independent and additive information regarding long-term prognosis.