Abstract Although conversion of atrial fibrillation (AF) to sinus rhythm can usually be accomplished by electrical or drug therapy, effective atrial systole may not be restored. To investigate the return of atrial transport function and its relation to the duration of the arrhythmia, Doppler echocardiography was performed after conversion in 18 patients with acute AF (<1 week duration), 14 patients with chronic AF (>1 week duration) and 15 control patients. Flow velocities during rapid filling (E wave) and atrial systole (A wave) were measured in both left and right ventricles. Patients in the acute AF group had left ventricular A waves (49 ± 4 cm/s) and A E ratios (0.97 ± 0.1) similar to those of the control patients (55 ± 7 cm/s, 0.87 ± 0.08, respectively). In contrast, patients in the chronic AF group had much smaller A waves (19 ± 5 cm/s) and A E ratios (0.30 ± 0.08) than those in the other 2 groups (p < 0.001). Five patients with chronic AF (36%) had complete left atrial paralysis ( A E = 0 ) despite normal sinus P waves. Measurements in the right ventricle showed similar differences among the groups. Patients with chronic AF who maintained sinus rhythm showed an increase in A E ratio to control levels, from 0.45 ± 0.1 to 0.93 ± 0.1 (p = 0.003) at 48 days (average) after conversion. Thus, atrial transport function is normal after brief periods of AF, but reduced or absent when conversion is achieved after the arrhythmia has been sustained >1 week. The mechanism is not known. Atrial contribution to filling gradually increases after conversion.