Decreased left ventricular (LV) function is a strong predictor of mortality. Although current guidelines recommend prophylactic implantable cardioverter-defibrillator (ICD) implantation after ST-elevation myocardial infarction and a depressed LV ejection fraction for 1 month, the prognoses of these patients may be better than those observed in randomized trials of ICDs (1-year mortality 6.8% to 19%), particularly because reperfusion treatment has improved, and the use of life-saving drugs is higher. To assess 1-year mortality in patients with depressed LV ejection fractions after primary percutaneous coronary intervention, a prospective, observational study was performed. Data from all patients who survived >/=30 days after primary percutaneous coronary intervention and had LV ejection fractions </=30% from 1994 to 2004 were recorded. Of 2,544 patients, 342 (13%) had LV ejection fractions </=30%. One-year mortality was 5.8%. Sudden death was the most common cause of death (40%). Patients who died more often had multivessel disease and a higher incidence of recurrent myocardial infarction within 1 year. In conclusion, current mortality in patients with depressed LV ejection fractions after primary percutaneous coronary intervention is much better than that observed in previous ICD trials, and the benefits of ICD therapy in these patients should be further evaluated.