Objectives Early recognition of acute myocardial infarction (AMI) and early activation of emergency medical services (EMS) are essential to reduce delays in patient care. We investigated public awareness of the need to call EMS at onset of AMI and evaluated associated factors. Methods In January 2008, a nationwide population-based survey using quota sampling was conducted in Japan. The primary outcome measure was responsiveness to promptly calling EMS at AMI onset, subdivided by on-time (daytime) and off-time (nights and holidays) hours. Results In total, 1200 participants were surveyed. Their mean age was 46.3 years (standard deviation, 17.4), and 50.3% (n=604) were women. A total of 11.6% (n=139) answered that they would call EMS during on-time hours, and 27.5% (n=330) stated that they would call during off-time hours. Multivariable analysis showed that the participants' age, female sex, education level, and self-confidence regarding their understanding of AMI were significant associated factors. The associated factors were almost identical during the off-time hours; only sex was no longer significant. Conclusions Public awareness of the need to call EMS at AMI onset in Japan was low. Previous intervention studies that were not effective may not have targeted groups with significant risk factors.