Chronic atrial fibrillation is the most common arrhythmia in patients with mitral valve disease, it not only deteriorates cardiac output, but also promotes a 5.6 times higher incidence of thromboembolic events. Nevertheless, the exact mechanism of atrial fibrillation is still poorly understood. Moreover, the long-term results of treatment, either by drugs or cardioversion, are almost always disappointing. Recent investigations suggest that atrial fibrillation is probably due to intraatrial multiple reentrant waves. It is also well-known from animal experiments that for sustenance of the fibrillation a critical mass of atrium is necessary. Based on these data, a new surgical method has been carefully designed to reduce atrial mass and to prevent sustenance of fibrillation. Between July and December 1988, five patients, one male and four females, with mitral valve disease and chronic atrial fibrillation were selected for this new surgical method. The age distribution ranged from 25 to 57 years, with a mean of 36 +/- 13 years. All of them had chronic atrial fibrillation which had been documented for more than one year. The operation was performed using the cardiopulmonary bypass and cardioplegia myocardial protection techniques. The left atrium was opened via the interatrial sulcus. After the mitral valve was repaired, cryosurgery (-60 degrees C for 120 sec) was applied along the borders of the left atrial free-wall. The left atrium was separated by these cryolesions into two sections, each about half the mass of the original and both sections were connected with a few atrial fibers located behind the coronary sinus. No surgical mortality or complications were encountered.(ABSTRACT TRUNCATED AT 250 WORDS)