The Medical Priority Dispatch System (MPDS) is a standardised system of protocols that assists ambulance dispatchers to identify chief complaints and assigning an appropriate emergency response. Callers reporting non-traumatic chest pain are allocated a protocol 10, the majority receive a Code-1(lights-and-sirens) response, and includes a tool that may result in self-administration of aspirin. However, the accuracy of protocol 10 correctly identifying acute coronary syndrome (ACS) is not well understood. We linked adult Victorian patients allocated a Protocol 10 between 2008 and 2015 to diagnoses from paramedics (in patients not transported), the Victorian Emergency Minimum Dataset (VEMD–in patients discharged from public ED), and the Victorian Admitted Episodes Dataset (VAED–in all patients admitted). Over this 8-year study, there were 350,169 Protocol 10 patients attended: 92% received a Code-1 response; 98% were transported to hospital; and 15% had a diagnosis of ACS. Among non-ACS cases there were 4492 different diagnoses, the most common being unspecified chest pain (37%), and 60% were admitted to hospital. Diagnoses where aspirin could be potentially harmful were rare but present (e.g. ruptured AAA, haemorrhage, SAH, GI bleeds). Chest pain is a broad presenting complaint, with many possible causes and ACS making up a small percentage. A significant proportion of patients reporting chest pain do not require a lights-and-sirens response, and for some aspirin may be harmful. Improving ambulance triage and the benefit/safety of aspirin administration in this group needs to be explored further.