Cardioversion of atrial fibrillation transiently increases the risk of embolism presumably by decreased atrial mechanical function. It has been suggested that a component of early dysfunction relates to the mode of cardioversion. Amiodarone is one of the drugs used to restore sinus rhythm in patients with atrial fibrillation. However, the effect of this drug on left and right atrial mechanical function after conversion to sinus rhythm is not well known. Thirty-one patients (group AF) cardioverted from atrial fibrillation with intravenous amiodarone (average dose 1 gm/day) were prospectively studied to examine the effect of this drug on recovery of left and right atrial mechanical function. These patients were compared with 17 consecutive individuals without evidence of cardiac disease who became our control group (group C). Transmitral flow velocities and echocardiographic parameters were recorded within 24 hours after cardioversion and on the seventh day in group AF and one time in group C. Left and right atrial ejection force to evaluate atrial mechanical function was defined as 0.5 x 1.06 x mitral (m) or tricuspid (t) orifice area x (m or t peak A velocity)2. If this value in group AF was more than the mean minus 1 standard deviation of control group data, atrial ejection function after cardioversion was considered normal. The two groups were similar with respect to age, sex, arterial blood pressure, heart rate, left ventricular diameters, and left ventricular ejection fraction. Left and right atrial size was higher in group AF (left: group AF, 18.1 +/- 3.9 cm2; group C, 11.3 +/- 2.5 cm2, p < 0.01; right: group AF, 14.9 +/- 3.2 cm2; group C, 11.6 +/- 2.3, p < 0.01). Measurements of right and left atrial ejection force measured within 24 hours and on day 7 in group AF were similar to that in group C (left: group C, 11.9 +/- 5.3 kdyne; AF group, 24 hours, 19.4 +/- 15.5 kdyne [NS]; AF group, day 7, 14.7 +/- 13.6 kdyne [NS]; right: group C, 3.6 +/- 1.99 kdyne; AF group, 24 hours, 4.3 +/- 3.3 kdyne [NS]; AF group, day 7, 3.5 +/- 2.9 kdyne [NS]). Therefore almost all patients undergoing cardioversion for atrial fibrillation with amiodarone recovered bilateral atrial mechanical function within 24 hours after cardioversion (26 of 31-84%-left atrial ejection force; 28 of 31-93.5%-right atrial ejection force), with normal left atrial function in 97% of patients and normal right atrial function in 100% of patients on day 7 after conversion to sinus rhythm. These findings may have significant implications on postcardioversion anticoagulation strategies.