Prompt recognition of symptoms and response to acute coronary syndrome (ACS) are crucial for reducing pre-hospital delay. This study compares culturally and linguistically diverse (CALD) and non-CALD Australian populations in terms of their (i) ACS symptom knowledge and (ii) intention to call emergency medical services (EMS) for ACS. This cross-sectional study used data from HeartWatch, an online survey collected by the National Heart Foundation of Australia between 2018 and 2020 for Australian adults aged ≥18 years. CALD respondents were defined as non-Indigenous individuals who reported speaking a language other than English at home. Characteristics associated with ACS symptom knowledge and EMS calling intentions were analysed using multivariable logistic regression. Of 31,919 respondents, 16.3% were from CALD backgrounds (n=5,212). Compared with non-CALD, CALD respondents were less likely to name any ACS symptom (63.0% vs 76.0%; adjusted odds ratio [AOR] 0.66; 95% confidence interval [CI] 0.61-0.70) and were less likely to state that they would call an ambulance for ACS (50.2% vs 72.1%; AOR 0.53; 95% CI 0.50-0.57). Almost one-quarter (23.0%) of CALD respondents reported not knowing what they would do. In both groups, males, individuals aged ≤60 years, and those with diabetes were less likely to name an ACS symptom and had lower intention to call an ambulance. Those unable to list a single ACS symptom also had a lower intention to call an ambulance. Knowledge of ACS symptoms and intention to call an ambulance were lower among CALD respondents. The demographics of those with low ACS symptom knowledge and EMS calling intention were similar in the two groups. Future education efforts in Australia should focus on promoting ACS symptom knowledge and EMS use and should target these groups.