A total of 15 patients with spontaneously arrested sustained atrial fibrillation (its duration 7.0 +/- 1.6 years) were followed up. After termination of atrial fibrillation, all the patients had signs of the sick sinus syndrome (profound sinus bradycardia, pacemaker migration, inferior atrial and atrioventricular rhythms). Thirteen of 15 patients suffered from rheumatic heart disease, nine of them had severe heart failure. Four patients immediately died. An atrial fibrillation relapse occurred in the immediate period in most cases, and rhythm recovery was unaccompanied by the improvement of the patients' condition.