Quinidine was combined with propranolol to restore sinus rhythm in cases of paroxysmal atrial fibrillation (PAF) in 42 patients. The treatment was started with propranolol and quinidine at a test oral dose of 10 mg and 0.2 g, respectively, thereafter a dose of 0.4 g of quinidine and 10 mg of propranolol every two hours was added. The procedure was stopped when sinus rhythm was achieved, or when the administered quinidine reached the total dose of 1.6 g. Sinus rhythm was restored in 37 patients. The side effects were gastrointestinal disorders in 16 patients, atypical ventricular tachycardia in one case, and embolism of the left femoral artery in another patient.