This study has compared the effect on heart rate control of the addition of pindolol 15 mg bd or verapamil 40 mg tds to maintenance digoxin therapy in 12 patients with chronic atrial fibrillation. The study was performed in a randomized cross-over fashion. Treatment effects were assessed by 24-h ambulatory electrocardiography and symptomatic improvement by symptom scores. The results show that the combination of pindolol and digoxin provides better control of atrial fibrillation. With an attenuation of daytime tachycardia, prevention of nocturnal bradycardia and reduction in the length of nocturnal pauses in rhythm. Overall heart rate variability was significantly less with digoxin and pindolol (523 beats min-1 h-1) than with digoxin and verapamil (745 beats min-1 h-1). We conclude that, in the dosages employed, combined digoxin and pindolol therapy is superior to either digoxin and verapamil in combination or digoxin alone for the treatment of atrial fibrillation.