ANTIARRHYTHMIC AGENTS (antidysrhythmic agents) are used to treat a number of heart conditions characterized by irregularities of heart beat. They have been classified under the Vaughan Williams Scheme, though not all clinically used agents neatly fit these classes.

Class I (which has a number of subtypes) is mainly used to treat atrial and ventricular tachycardias, and contains a number of SODIUM-CHANNEL BLOCKERS, e.g. disopyramide, flecainide, lignocaine, procainamide and quinidine.

Class II, which is valuable for stress-induced tachycardias, contains β-ADRENOCEPTOR ANTAGONISTS, e.g. metoprolol, propranolol.

Class III, which is used for certain tachycardia syndromes, includes amiodarone (whose mechanism of action is not clear), POTASSIUM-CHANNEL BLOCKERS and the atypical β-blocker sotalol.

Class IV is used for atrial tachyarrhythmias and contains certain CALCIUM-CHANNEL BLOCKERS, e.g. diltiazem and verapamil.

In addition to drugs in these classes, others may be used for certain arrhythmias. Digoxin may be used for treatment of atrial fibrillation, adrenaline for asystolic cardiac arrest, atropine for sinus bradycardia, methacholine (rarely) for supraventricular tachycardia, magnesium salts for ventricular arrhythmias, and calcium salts for ventricular arrhythmia due to hyperkalaemia.