To determine if the return of atrial contraction as evidenced by progressive return of the A wave on the Doppler atrial profile could better predict long-term success of cardioversion than other clinical and echocardiographic parameters, 50 patients were studied 4 hours, 24 hours and, if sinus rhythm persisted, up to 180 days after cardioversion. Recurrence of atrial fibrillation (AF) was 64% at 6 months. Age, sex, prior episodes of AF, presence of mitral valve disease or magnitude of mitral valve gradient did not predict recurrence, but duration of AF was significantly longer in the failure group (p less than 0.01). Left atrial dimension greater than or equal to 45 mm had a positive predictive value of 66%, with a sensitivity of 59% and a specificity of 61%. Presence or magnitude of the A wave at 4 hours did not predict long-term success of cardioversion. Percent increase of the A wave from 4 to 24 hours less than 10% had the highest positive predictive value (80%) for recurrence of AF (sensitivity 71% and specificity 71%) and can be obtained in the immediate post-cardioversion period to better establish prognosis and adjust therapeutic regimens.