In 2005, approximately 920,000 persons in the United States had a myocardial infarction (i.e., heart attack); in 2004, approximately 157,000 heart attacks were fatal. One study indicated that approximately half of cardiac deaths occur within 1 hour of symptom onset, before patients reach a hospital. Timely access to emergency cardiac care, receipt of advanced treatment, and potential for surviving a heart attack all depend on 1) early recognition of warning signs and symptoms of a heart attack by persons who are having a heart attack and bystanders and 2) immediately calling 9-1-1. Healthy People 2010 includes an objective to increase from 46% to 50% the proportion of adults aged > or =20 years who are aware of the early warning signs and symptoms of a heart attack and the importance of accessing rapid emergency care by calling 9-1-1 (objective 12-2). To update estimates of public awareness of heart attack warning signs and symptoms and knowledge of the importance of calling 9-1-1, CDC analyzed 2005 Behavioral Risk Factor Surveillance System (BRFSS) data from the 14 states that included questions on signs and symptoms of a heart attack. This report describes the results of that analysis, which indicated that although the awareness of certain individual warning signs was as high as 93% (i.e., for shortness of breath), awareness of all five warning signs was 31%, underscoring the need for public health measures to increase public awareness of heart attack warning signs and symptoms. In addition, disparities in awareness were observed by race/ethnicity, sex, and level of education, suggesting that new public health measures should target populations with the lowest levels of awareness.