Editing Antiarrhythmic agent (section)

===Class III agents===
[[Image:Action potential Class III.svg|thumb|class=skin-invert-image|Effect of class III drugs on length of action potential]]
Class III agents predominantly [[Potassium channel blocker|block the potassium channels]], thereby prolonging repolarization.<ref>{{cite journal | last1 = Lenz | first1 = TL | last2 = Hilleman | first2 = DE | year = 2000 | title = Dofetilide, a New Class III Antiarrhythmic Agent | pmid = 10907968 | journal = Pharmacotherapy | volume = 20 | issue = 7| pages = 776–786 | doi=10.1592/phco.20.9.776.35208| s2cid = 19897963 }}</ref> Since these agents do not affect the sodium channel, conduction velocity is not decreased. The prolongation of the action potential duration and refractory period, combined with the maintenance of normal conduction velocity, prevent re-entrant arrhythmias. (The re-entrant rhythm is less likely to interact with tissue that has become refractory). The class III agents exhibit reverse-use dependence (their potency increases with slower heart rates, and therefore improves maintenance of sinus rhythm). Inhibiting potassium channels results in slowed atrial-ventricular myocyte repolarization. Class III agents have the potential to prolong the QT interval of the EKG, and may be proarrhythmic (more associated with development of polymorphic VT).

Class III agents include: [[bretylium]], [[amiodarone]], [[ibutilide]], [[sotalol]], [[dofetilide]], [[vernakalant]], and [[dronedarone]].