The antiarrhythmic efficacy of Cordarone was studied in 90 patients (64 men and 26 women) aged 16-76. Cordarone appeared to be efficacious in the treatment of resistant arrhythmias, particularly ventricular extrasystoles and paroxysmal tachycardia in the WPW syndrome. Total disappearance of dysrhythmias was achieved in 40%, and good therapeutic effects in 32% of patients (an overall 72 percent success). Rapid initial loading (800-1200 mg/day) and continuation with a maintenance dose (100-400 mg/day) may be used as an optimal therapy model. Cordarone is well tolerated even with prolonged use. Side-effects necessitated drug withdrawal in 4.4% of patients. It is possible to combine Cordarone with other selected antiarrhythmic drugs in most resistant rhythm disturbances.