The heart rate increase induced by dynamic exercise in patients with chronic atrial fibrillation is competitively attenuated by beta-blockade. The influence of oral celiprolol on exercise induced tachycardia was evaluated in 23 patients with chronic stable atrial fibrillation in a dose-titration study. This was succeeded by a placebo-controlled double-blind, crossover multi-center trial. During the dose-titration phase each patient underwent a single-blind three week dose escalation period-taking celiprolol 200 mg once daily for one week, celiprolol 400 mg once daily for the third week. After a one week placebo washout, patients then entered a double-blind crossover phase, consisting of one week each of placebo or celiprolol according to a pre-determined randomization. After one week of placebo washout, each patient was crossed-over. In 21 patients celiprolol reduces exercise-induced increased heart rate by approximately 35% when compared with placebo. These results indicate that celiprolol should be effective in controlling the exercise-induced increase in heart rate in patients with chronic atrial fibrillation. In addition, results of 24 h ambulatory ECG monitoring (Holtor monitoring) indicate that celiprolol reduces the ventricular premature contractions.