A sodium channel blocker and class Ib antiarrhythmic agent; inhibits aconitine-induced dysrhythmias in mice (ED50s = 57 and 107 mg/kg for i.p. and oral administration, respectively); decreases or inhibits conduction across the Purkinje fiber-muscle junction in isolated canine Purkinje fiber and ventricular muscle preparations when used at concentrations of less than 5 μg/ml