BACKGROUND Higher-risk patients may not receive evidence-based therapy because of limited life expectancy, which is a composite measure that encompasses many patient factors, including age, frailty, and comorbidities. In this study, we evaluated the extent to which treatment care gaps can be explained by a difference in projected life expectancy. RESULTS An observational cohort study was conducted on acute myocardial infarction patients hospitalized in Ontario, Canada. Projected life expectancy was estimated using actual survival data with extrapolation using proportional hazard models adjusting for important covariates. The relationship between projected life expectancy with statins and reperfusion therapy was examined using generalized linear models. Among the 7001 acute myocardial infarction patients, 84.3% were prescribed statins and 72.9% were treated with reperfusion therapy. When projected life expectancy was <10 years, the likelihood of receiving either treatment declined progressively with reduction in life expectancy (P<0.001). At the 25th percentile of projected life expectancies, the likelihood of receiving a statin decreased by 1.4% (95% confidence interval, 1.0-1.8%), and acute reperfusion therapy decreased by 2.6% (95% confidence interval, 1.8-3.3%) for each year decline in projected life expectancy. CONCLUSIONS Life expectancy of a patient strongly influences evidence-based treatment in acute myocardial infarction. It was seen not only among patients with limited life expectancies but also among those with many years to live. Treatment care gaps may reflect clinicians' synthesis about frailty and life-expectancy gains.