The IMMEDIATE Trial of very early intravenous glucose-insulin-potassium (GIK) for acute coronary syndromes (ACS) in out-of-hospital emergency medical service (EMS) settings showed 80% reduction in infarct size at 30 days, suggesting potential longer-term benefit. Here we report 1-year outcomes. Pre-specified 1-year endpoints of this randomized, placebo-controlled, double-blind, effectiveness trial included all-cause mortality, and composites including cardiac arrest, mortality, or hospitalization for heart failure (HF). Among 871 participants randomized to GIK vs. placebo, respectively, death occurred within 1 year in 11.6% vs. 13.5% (unadjusted hazard ratio [HR] 0.83; 95% CI 0.57, 1.23, P=0.36). The composite of cardiac arrest or 1-year mortality was 12.8% vs. 17.0% (HR 0.71; 95% CI 0.50, 1.02, P=0.06). The composite of hospitalization for HF or mortality within 1 year was 17.2% vs. 17.2% (HR 0.98; 95% CI 0.70, 1.37, P=0.92). The composite of mortality, cardiac arrest, or HF hospitalization within 1 year was 18.1% vs. 20.4% (HR 0.85; 95% CI 0.62, 1.16, P=0.30). Among patients presenting with suspected ST elevation myocardial infarction (STEMI), hazard ratios for 1-year mortality and the 3 composites were, respectively, 0.65 (95% CI 0.33, 1.27, P=0.21); 0.52 (95% CI 0.30, 0.92, P=0.03); 0.63 (95% CI 0.35, 1.16, P=0.14); and 0.51 (95% CI 0.30, 0.87, P=0.01). Among patients with suspected ACS, serious endpoints generally were lower with GIK than placebo, but the differences were not statistically significant. However, among those with STEMI, the composites of cardiac arrest or 1-year mortality, and of cardiac arrest, mortality, or HF hospitalization within 1 year, were significantly reduced.