QUESTION UNDER STUDY: To explore whether early activation of an interventional cardiology team, by prehospital emergency physicians, reduces door-to-balloon time (DTBT) in patients with ST-elevation myocardial infarction (STEMI) diagnosed with prehospital ECG. METHODS: Design: before-after comparison. Setting: emergency department (ED) of an urban teaching hospital with a catheterisation laboratory open continuously. Study subjects: patients with STEMI diagnosed in the prehospital setting or in the ED within 12 hours of symptoms. Intervention: a paging system or "STEMI alarm", activated by prehospital physicians, which simultaneously notified both the catherisation laboratory and cardiology teams before the patient's arrival to the ED. Outcome measures: DTBT and the proportion of patients with DTBT <90 minutes. RESULTS: A total of 196 patients were included; 77 before and 119 after implementation of the "STEMI alarm". Between the two periods, median DTBT decreased from 109 to 76 minutes (p <0.001) and the proportion of patients treated within 90 minutes increased from 36% to 66% (p <0.001). During intervention, the STEMI alarm was activated in 67 patients (56%). In these cases the median DTBT was 50 minutes, with 96% within 90 minutes. The alarm was inappropriately activated in 9 cases (11%). CONCLUSIONS: Catheterisation laboratory activation by a prehospital emergency physician markedly reduces DTBT in STEMI patients.