In the examination of 120 patients without valvular heart disease suffering from atrial fibrillation paroxysms mechanical function of the left atrium (LA) was assessed using Doppler echocardiography. The majority of the examinees had dilated LA which is thought to be arrhythmogenic. The recovery of the sinus rhythm is accompanied by electromechanical dissociation the longest duration of which took place in subjects exposed to electrical defibrillation. An inverse relationship was established between the time of the last fibrillation and recovery of LA mechanical function. The duration of the electromechanical dissociation of the atria holds prognostic importance in relation to recurrent fibrillation.