Amiodarone is a class III antiarrhythmic agent, in that it prolongs both cardiac action potential and refractoriness by blocking potassium currents. It inhibits the voltage-gated potassium channel hERG, also known as KCNH2, with an IC50 value of 1 µM. In humans, cytochrome P450 3A is involved in the metabolism of amiodarone. N-Desethylamiodarone is the major, active metabolite of amiodarone. This compound has been used as an analytical reference standard for quantifying amiodarone in plasma samples.