Many individuals in the United States remain unaware of the symptoms of and appropriate response to a myocardial infarction (MI). In this cross-sectional study of 25,271 adults, 5.8 percent were not aware of any MI symptoms, and 4.5 percent chose an action other than calling EMS, in response to these symptoms. Prompt recognition of MI symptoms is critical for timely access to lifesaving emergency cardiac care. However, patients with MI continue to have a delayed presentation to the hospital. In this study, several sociodemographic subgroups were associated with a higher risk of being unaware of symptoms and response. They may benefit the most from targeted public health initiatives.