The incidence of atrial fi brillation has been rapidly increasing in recent years. The increased tonus of the sympathetic nervous system is related to the development of atrial fi brillation. OBJECTIVE: To study the effect of bisoprolol, a highly selective beta-blocker, on patients with recent-onset atrial fi brillation (< 48 hours) for regularization of the rhythm using propafenone. PATIENTS AND METHODS: The study includes 164 patients (81 women, 83 men, age 59.09 ± 10.81) with successfully restored sinus rhythm in recent-onset atrial fi brillation. The patients received either propafenone (group A, n = 82) or a combination of propafenone and bisoprolol (group B, n = 82). The studied patients were randomly allocated to the groups. Propafenone was administered intravenously as a 2 mg/kg bolus followed by infusion of 0.0078 mg/kg/min for 120 min and orally in dosage of 300 mg three times every 8 hours if arrhythmia persisted. Bisoprolol was administered in a single dose at the very beginning of propafenone treatment and only in patients from group B at a dose of 5 or 10 mg. Regularization of the rhythm was assessed at the 3rd, 6th, 12th and 24th hour. RESULTS: In the initial stages of regularization the combined therapy restored the sinus rhythm in a greater number of patients in comparison with the monotherapy (at the 6th hour 67.07% in group B versus 48.78% in group A, P < 0.05; at the 12th hour it was 87.80% versus 75.60%, respectively, P < 0.05). CONCLUSION: Early regularization of rhythm in patients with recent-onset atrial fi brillation reduces the likelihood of recurrent episodes of arrhythmia. This makes the application of selective beta-blockade clinically signifi cant.