Fifteen years after the introduction of beta adrenergic blocking drugs into clinical medicine, there is satisfactory evidence indicating that this class of drug has significant anti-arrhythmic activity. The chief indications for using these drugs are for the control of sinus tachycardia digitalis dysrhythmias and for the control of rapid ventricular rates atrial and ventricular dysrhythmias. The mode of action is by antagonizing the cardiac actions of catecholamines on cardiac automaticity and conduction.