The class 1c drugs include flecainide, propafenone and moricizine. They share with the class 1a drugs the ability to block the sodium channel in normal as well as diseased cells and by this mechanism, lengthen QRS duration. However, unlike the class 1a drugs, they do not exert a significant effect on the potassium channels and therefore do not have significant effect on the ST segment or T wave. Propafenone is also a weak beta-adrenergic blocking agent.