BACKGROUND Incidence, characteristics and predictive factors of transient ST-segment changes after DC shock are poorly known. METHODS 91 consecutive pts referred for external cardioversion of atrial fibrillation (AF) (61 men, 69±10 yo) were prospectively included. The presence of ST elevation or depression was assessed on 12 lead-ECG immediately after the first DC shock. Correlations with DC shock characteristics (monophasic/biphasic and energy), clinical variables, echocardiographic parameters, biological parameters, medications, anaesthetic drugs as well with morphological features were made. RESULTS 18 and 20 pts underwent 200 J or 300 J monophasic and 53 pts 200 J biphasic DC shocks. We found an incidence of 48% for ST-segment changes: 35% for ST elevation and 13% for ST depression. ST changes did not induce significant cardiac events or alter AF recurrences. ST changes were not related to energy but ST elevation was significantly more often induced by monophasic (76% vs 6%, p<0.0001) and ST depression by biphasic DC shocks (26% vs 3%, p=0.01). Using multivariate analysis, independent predictors for ST elevation were the use of monophasic DC shocks, of propofol and increased CRP, while a low ejection fraction and use of biphasic DC shocks were independent predictors of ST depression. CONCLUSIONS ST-segment changes after external cardioversion with DC shock are common, short living and do not carry clinical significance. They are related to the monophasic or biphasic configuration of DC shock, to the use of propofol, to the ejection fraction and to an increased CRP.