Although several advances have been made in the management of acute coronary syndromes, the adoption of such measures in clinical practice has been suboptimal. The implementation of critical pathways has been suggested as a strategy to improve clinical effectiveness, although its effect is still to be demonstrated. The objective was to evaluate the impact of a critical pathway on the process of care of patients admitted with acute coronary syndromes in a teaching hospital. In a prospective cohort study, patients 30 years or older admitted to the emergency department with suspected acute coronary syndromes were evaluated. Primary outcomes were major cardiovascular events, percutaneous coronary intervention, and in-hospital mortality during 1 semester before and 4 semesters after implementation of the pathway. Multivariate logistic regression analysis was used to adjust for differences between the periods studied and to identify predictors of poor prognosis. Of the 1003 patients evaluated, 150 (15%) had myocardial infarction, and 240 (24%) had unstable angina. There was no difference in clinical characteristics and risk assessment in the periods evaluated. Overall, the quality of care improved after the pathway, with a significant decrease in complication and mortality rates in the last 2 years. In multivariate analysis, patients admitted in the last semester showed fewer major cardiovascular events (odds ratio = 0.74; P = 0.02) and more percutaneous coronary intervention (odds ratio = 1.3; P = 0.03). The implementation of a critical pathway may have a positive impact on the quality of care of patients with acute coronary syndromes. Further studies are needed to evaluate better this and other initiatives aimed at maximizing clinical effectiveness.