BACKGROUND AND OBJECTIVES: Epidemiologic studies and clinical trials require a more precise definition of acute myocardial infarction (AMI). The advent of sensitive and specific serologic biomarkers can identify those patients with small areas of myocardial necrosis. Acute myocardial infarction was redefined and approved by the ESC/ACC on September, 2000. To investigate the clinical implications of the revised criteria, the clinical features, the in-hospital outcomes and the 18 months outcomes were compared between the AMI patients who were diagnosed using the definition of the WHO criteria and those AMI patients added by the revised criteria. SUBJECTS AND METHODS: One hundred and seventy four consecutive patients diagnosed as AMI by the new criteria were included in the study. These patients with positive cardiac enzymes and ischemic symptoms or signs (n=174) were divided into two groups. The patients of group 1 (n=105) were the patients who were diagnosed with AMI by the WHO criteria, and the patients of group 2 (n=69), were the additional patients who were diagnosed with AMI only by the new criteria. RESULTS: The new criteria of AMI by ESC/ACC increased the numbers of AMI by 66%. As compared with group 1, women and patients with hypertension and a past history of ischemic heart disease were more common in group 2 (p<0.05). Percutaneous coronary intervention (PCI) was used less frequently and Angiotensin converting enzyme inhibitors (ACEIs), beta blockers and aspirin were prescribed less frequently in group 2. The total cardiac events and cumulative survival rate in group 1 were higher than in Group 2 (12.3% vs 7.2%, 89% vs 94%, respectively) but these differences were not statistically significant. CONCLUSION: The new criteria results in a substantial increase in the diagnosis of AMI, and the new criteria helps identify patients who were missed by the old criteria. The patients with AMI who were added by the new criteria had a similar risk of adverse outcome.