Objectives We sought to assess the impact of the American College of Cardiology’s Guidelines Applied in Practice (GAP) project for acute myocardial infarction (AMI) care, encompassing 33 acute-care hospitals in southeastern Michigan, on rates of mortality in Medicare patients treated in Michigan. Background The GAP project increases the use of evidence-based therapies in patients with AMI. It is unknown whether GAP also can reduce the rate of mortality in patients with AMI. Methods Using a before (n = 1,368) and after GAP implementation (n = 1,489) cohort study, 2,857 Medicare patients with AMI were studied to assess the influence of the GAP program on mortality. Multivariate models tested the independent impact of GAP after controlling for other conditions on in-hospital, 30-day, and one-year mortality. Results Average patient age was 76 years, 48% were women, and 16% represented non-white minorities. The rate of mortality decreased after GAP for each interval studied: hospital, 10.4% versus 13.6%; 30-day, 16.7% versus 21.6%; and one-year, 33.2% versus 38.3%; all p < 0.02. After multivariate adjustment, GAP correlated with a 21% to 26% reduction in mortality, particularly at 30 days (odds ratio of GAP to baseline 0.74; 95% confidence interval [CI] 0.59 to 0.94; p = 0.012) and one year (odds ratio 0.78; 95% CI 0.64 to 0.95; p = 0.013), particularly in the patients for whom a standard discharge tool was used (1-year mortality, odds ratio 0.53; 95% CI 0.36 to 0.76; p = 0.0006). Conclusions Embedding AMI guidelines into practice was associated with improved 30-day and one-year mortality. This benefit is most marked when patients are cared for using standardized, evidence-based clinical care tools.