Effect of verapamil on experimental arrhythmias

Verapamil 0.25-1.0 mg/kg i.v. did not significantly elevate the ventricular fibrillation threshold in dogs. It did not antagonize the deslanoside arrhythmias, but inhibited transiently the arrhythmias induced by either electrical stimulation of the posterior hypothalamus or bilateral carotid occlusion in cats. Effect of verapamil on the aconitine-induced rapid firing of the isolated atria and ventricles of the young rabbit and chick embryos was also studied with the microelectrode technique. In doses of 5, 10 and 20 microng/ml, it suppressed the rapid firing of the cardiac preparations, with exception of the ventricles of the rabbit. Antiarrhythmic action of verapamil in such high concentration seems to be due to non-specific inhibitions of Na+ channels of the myocardial cells.