Disopyramide is a sodium channel blocker that, in rabbit ventricular myocytes, binds and dissociates from open channels more quickly than from resting channels. It is a class Ia antiarrhythmic agent that delays conduction through the AV node and ventricles of the dog heart both in vivo (3 and 5 mg/kg) and in vitro (1-2 mg/L). Formulations containing disopyramide have been used in the treatment of cardiac arrhythmias and hypertrophic cardiomyopathy.