Effects of Optical Isomers of Verapamil on SA Nodal Pacemaker Activity and Contractility of the Isolated Dog Heart

Using 10 isolated, blood-perfused canine atrial, and ventricular preparations, the effects of d- and l-verapamil on SA nodal pacemaker activity and contractility were investigated. l-verapamil and d-verapamil produced dose-related negative chronotropic and inotropic effects in all experiments. l-verapamil was approximately 10 times more potent than d-verapamil both in inotropism and chronotropism. Negative inotropism of either d- or l-verapamil can be reversed by injection of calcium chloride. Not only d-verapamil but also l-verapamil produced a stronger suppression at higher frequencies in both atrial and ventricular muscles.