An epidemic of coronary heart disease (CHD) began during the 20th century in most industrialized countries, where CHD is a leading cause of mortality among adults. 1 Developing countries show the beginnings of the same epidemic. Reliable information on population incidence, prevalence, and case-fatality rates of CHD is essential to understanding, treating, and controlling the epidemic but is generally unavailable. Consistent and universal definitions of cases of CHD allow the determination of rates and comparisons within and between populations. These case definitions are essential to epidemiological studies and other research, such as clinical trials, quality assurance, and economic analysis of healthcare costs. The need for standardization is clear, and this statement recommends updated definitions. Definitions of cases for epidemiology studies and clinical trials in acute CHD rest on World Health Organization (WHO)(1959) and American Heart Association (1964) reports, followed by the WHO European AMI Registry criteria. 2, 3 Myocardial infarction (MI) is based on cardiac symptoms, ECG changes, and/or elevation in biomarkers. This basic system has been widely used but variably interpreted, resulting in a lack of comparability among and within studies. Further specification and working definitions of CHD come from the Framingham Study. 4 The WHO criteria were revised in a joint report with the International Society and Federation of Cardiology in 1979. 5 More recently, the WHO MONICA Study6 and other surveillance and intervention studies, such as the Lipid Research Clinics in the United States, 7 have modified further the definition of CHD cases. These changes are usually based on a greater specification to the original WHO definition to allow for application in different settings.

Advancing diagnostic technology, therapeutic interventions, and changing disease presentation in recent years forces a reevaluation of case definitions for acute CHD. New biomarkers, cardiac troponins, and creatine kinase (CK)-MB mass provide information that is more sensitive and/or specific in detecting even minor myocardial cell damage. 8 New imaging methods, such as MRI and radioisotope imaging, although not widely available today, will add to the diagnostic tools. These developments were recently reviewed in a Joint European Society of Cardiology/American College of Cardiology Workshop on the Redefinition of Myocardial Infarction. 9 That report, published in 2000, provided direction for clinicians faced with changing diagnostic testing and new information. Another recent report extends advice to clinical trials. 10 However, they fall short of providing direction for epidemiologists faced with evaluating and interpreting trends in event rates on the basis of retrospective surveillance. Patterns of CHD presentation are also changing. Whether because of changes in disease severity, improved diagnostic testing, increased professional awareness of the diagnosis, heightened public awareness of CHD symptoms, or insurance reimbursement to hospitals, cases of CHD in hospitalized