Despite its recommendation by the current guidelines, the role of long-term oral beta-blocker therapy has never been evaluated by randomized trials in uncomplicated ST-segment elevation myocardial infarction (STEMI) patients without heart failure, left ventricular dysfunction or ventricular arrhythmia who underwent primary percutaneous coronary intervention (PCI). In a multi-center, open-label, randomized controlled trial, STEMI patients with successful primary PCI within 24 hours from the onset and with left ventricular ejection fraction (LVEF) ≥40% were randomly assigned in a 1-to-1 fashion either to the carvedilol group or to the no beta-blocker group within 7 days after primary PCI. The primary endpoint is a composite of all-cause death, myocardial infarction, hospitalization for heart failure, and hospitalization for acute coronary syndrome. Between August 2010 and May 2014, 801 patients were randomly assigned to the carvedilol group (N = 399) or the no beta-blocker group (N = 402) at 67 centers in Japan. The carvedilol dose was up-titrated from 3.4±2.1 mg at baseline to 6.3±4.3 mg at 1-year. During median follow-up of 3.9 years with 96.4% follow-up, the cumulative 3-year incidences of both the primary endpoint and any coronary revascularization were not significantly different between the carvedilol and no beta-blocker groups (6.8% and 7.9%, P = 0.20, and 20.3% and 17.7%, P = 0.65, respectively). There also was no significant difference in LVEF at 1-year between the 2 groups (60.9±8.4% and 59.6±8.8%, P = 0.06). Long-term carvedilol therapy added on the contemporary evidence-based medications did not seem beneficial in selected STEMI patients treated with primary PCI. CAPITAL-RCT (Carvedilol Post-Intervention Long-Term Administration in Large-scale Randomized Controlled Trial) ClinicalTrials.gov.number, NCT 01155635.