Disopyramide hydrochloride is a class IA antiarrhythmic agent with efficacy in ventricular and atrial arrhythmias. Disopyramide hydrochloride blocks the fast inward sodium current of cardiac muscle and prolongs the duration of cardiac action potentials. Disopyramide hydrochloride inhibits HERG encoded potassium channels. Disopyramide hydrochloride also exhibits complex protein binding, and has a potent negative inotropic action.