Part IV: Class II, Class III, and Class IV antiarrhythmic drugs, comparative efficacy of drugs, and the effect of drugs on mortality — review of their pharmacokinetics, efficacy, and toxicity. This part reviews the Class II antiarrhythmic agents that share the property of beta adrenergic antagonism, but include several drugs with other unique features. Also reviewed are the Class III agents, which prolong the action potential duration, with a focus on amiodarone. The Class IV agents, which antagonize the calcium channel, are reviewed. Finally, this part reviews the comparative efficacy of antiarrhythmic agents for treatment of ventricular ectopic depolarizations and examines their effect on mortalit