During the pre-event smallpox vaccination program, the U.S. Department of Defense (DOD) and CDC have received reports of cardiac events after vaccination. A case definition for myo/pericarditis as a smallpox vaccine--associated adverse event has been developed in conjunction with DOD, the joint Smallpox Vaccine Safety Working Group of the Advisory Committee on Immunization Practices (ACIP) and the Armed Forces Epidemiology Board (AFEB), and consulting cardiologists, immunologists, and epidemiologists. The term myo/pericarditis is used for surveillance purposes to refer to patients who have myocarditis, pericarditis, or both (myopericarditis). Myo/pericarditis cases are classified into suspected, probable, and confirmed categories. Suspected cases include those that are investigated and reported, although the level of certainty for the diagnosis is lower. These definitions were used to categorize all cardiac-related reports among civilian vaccinees received through May 9, 2003; a total of 21 cases of myo/pericarditis were ascertained. All have been reported previously; however, some have been reclassified. In addition, nine cases of ischemic cardiac events (i.e., myocardial infarction [MI] or angina) among civilian vaccinees have been reported previously. This report includes the case definition of myo/pericarditis and updates information on all reports of cardiac adverse events among 36,217 civilian vaccinees since the beginning of the civilian smallpox vaccination program reported through May 9 to CDC from the Vaccine Adverse Event Reporting System (VAERS).