Elapsed time from symptom onset and acute myocardial infarction in a community hospital. STUDY OBJECTIVE: Previous reports have emphasized that thrombolytic therapy for acute myocardial infarction should be initiated within three or four hours of symptom onset to obtain the best clinical outcomes. However, our clinical impression was that late arrivers, who often do not receive thrombolytic therapy, have a good short-term prognosis. Therefore, we investigated the relationships among the elapsed time from symptom onset, thrombolytic therapy, and short-term prognosis in acute myocardial infarction patients. The research hypothesis was that late arrivers have a better in-hospital prognosis because they have less severe disease that may involve spontaneous thrombolysis. DESIGN: Observational cohort study based on reviewing medical records and emergency department service logs. SETTING: 500-bed teaching hospital with medical school affiliation in northeastern Ohio. TYPE OF PARTICIPANTS: Four hundred consecutive patients with acute infarction confirmed by chest pain and positive ECGs or elevated cardiac enzymes. MEASUREMENTS AND MAIN RESULTS: Patients arriving early (elapsed time less than or equal to 1.5 hours) were more likely to be in Killip class III or IV (P = .04) or to have hypotension (P = .0004); and they experienced twofold increased odds of ventricular tachycardia (P = .007), cardiac arrest (P = .03), or death (P = .01). Patients arriving late (elapsed time greater than 3.5 hours) were more likely to have a history of angina (P = .002) and had a better short-term prognosis. CONCLUSIONS: Time of ED arrival after onset of acute myocardial infarction symptoms distinguishes two patient groups that differ in their risk of in-hospital complications. Late arrivers have better short-term prognoses and less (acutely) severe disease, and may have less need for thrombolytic therapy because of possible spontaneous thrombolysis. Patients with prior angina may need education on seeking care if their symptoms change. 