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BackgroundThe optimal duration of β‐blocker therapy in patients with acute myocardial infarction (AMI) is unknown. We aimed to evaluate the late effect of β‐blockers in patients with AMI. Methods and ResultsWe enrolled all consecutive patients who presented with AMI at Seoul National University Bundang Hospital, between June 3, 2003 and February 24, 2015. The primary end point was 5‐year all‐cause mortality, depending on the use of β‐blockers at discharge, 1 year after AMI, and 3 years after AMI. Of 2592 patients, the prescription rates of β‐blockers were 72%, 69%, 63%, and 60% at discharge and 1, 3, and 5 years after AMI, respectively. The patients who were receiving β‐blocker therapy had more favorable clinical characteristics, such as younger age (62 versus 65 years; P<0.001). They received reperfusion therapy more often (92% versus 80%; P<0.001) than those without β‐blocker prescription. In the univariate analysis, the patients with β‐blocker prescription had lower 5‐year mortality at all time points. In the Cox model after adjustment for significant covariates, β‐blocker prescription at discharge was associated with a 29% reduced mortality risk (hazard ratio, 0.71; 95% confidence interval, 0.55–0.90; P=0.006); however, β‐blocker prescriptions at 1 and 3 years after AMI were not associated with reduced mortality. ConclusionsThe beneficial effect of β‐blocker therapy after AMI may be limited until 1 year after AMI. Whether late β‐blocker therapy beyond 1 year after AMI offers clinical benefits should be confirmed in further clinical trials.