Amiodarone and sotalol are class III antiarryhythmic drugs that block membrane potassium channels, and have been available for many years. Newer class III antiarrhythmic drugs are now being developed, because they could circumvent several of the problems found with the more widely used class I, or sodium channel-blocking drugs. Class III drugs can be arrhythmogenic, but they might cause fewer arrhythmias than sodium channel-blocking drugs. As they do not affect the sodium channel, it is possible that they could have smaller effects on conduction velocity and contractility. For these reasons, class III drugs likely will assume an important role in the treatment of perioperative arrhythmias.