Class III antiarrhythmic drugs prolong action potential duration by blocking cardiac potassium channels. Amiodarone and d-1 sotalol are representative class III drugs commonly used for drug resistant arrhythmias. Amiodarone has miscellaneous properties including potassium, sodium, calcium, and nonspecific sympathetic blocking effects when it is given orally. It mainly blocks sodium channels when it's given intraveneously. Amiodarone requires careful follow up because of its important side effects. Some randomised studies are still ongoing to confirm whether amiodarone can improve mortality in patients with refractoly ventricular arrhythmias.