BACKGROUND: Greater use of thrombolysis for patients with myocardial infarction has been limited by patient delay in seeking care for heart attack symptoms. Deficiencies in knowledge of symptoms may contribute to delay and could be a target for intervention. We sought to characterize symptom knowledge. METHODS: Rapid Early Action for Coronary Treatment is a community trial designed to reduce this delay. At baseline, a random-digit dialed survey was conducted among 1294 adult respondents in the 20 study communities. Two open-ended questions were asked about heart attack symptom knowledge. RESULTS: Chest pain or discomfort was reported as a symptom by 89.7% of respondents and was thought to be the most important symptom by 56.6%. Knowledge of arm pain or numbness (67.3%), shortness of breath (50.8%), sweating (21.3%), and other heart attack symptoms was less common. The median number of correct symptoms reported was 3 (of 11). In a multivariable-adjusted model, significantly higher mean numbers of correct symptoms were reported by non-Hispanic whites than by other racial or ethnic groups, by middle-aged persons than by older and younger persons, by persons with higher socioeconomic status than by those with lower, and by persons with previous experience with heart attack than by those without. CONCLUSIONS: Knowledge of chest pain as an important heart attack symptom is high and relatively uniform; however, knowledge of the complex constellation of heart attack symptoms is deficient in the US population, especially in low socioeconomic and racial or ethnic minority groups. Efforts to reduce delay in seeking medical care among persons with heart attack symptoms should address these deficiencies in knowledge.