Objective To assess the incidence of prognostically important myocardial damage in patients with chest pain discharged from the emergency department. Design Prospective observational study. Setting District general hospital emergency department. Participants 110 patients presenting with chest pain of unknown cause who were subsequently discharged home after cardiac causes of chest pain were ruled out by clinical and electrocardiographic investigation. Interventions Patients were reviewed 12-48 hours after presentation by repeat electrocardiography and measurement of cardiac troponin T. Main outcome measures Incidence of missed myocardial damage. Results Eight (7%) patients had detectable cardiac troponin T on review and seven had concentrations >0.1 g/l. The repeat electrocardiogram showed no abnormality in any patient. Conclusion 6% of the patients discharged from the emergency department had missed prognostically important myocardial damage. Follow up measurement of cardiac troponin T allows convenient audit of clinical performance in the emergency department.