Cardiovascualar effects of a verapamil infusion were investigated in six dogs given nalbuphine-nitrous anesthesia. Verapamil 0.2 mg/kg was given followed by an infusion of 3 and 6 mcg/kg per minute. Verapamil significantly reduced the systemic vascular resistanee index and mean arterial pressure. The decrease in afterload led to an increase in cardiac index, since was little change in myocardial contractility(LV dp/dt). Administration of calcium chloride, 20 mg/kg, did not reverse tbe hemodynamic effects of verapamil. The data indicate that in dogs verapamil be even in high concentrations, during nalbuphine-nitrous oxide anesthesia without serious adverse hemodynamic sequences.