Ten dogs were studied to determine the effects of xylazine, ketamine, and xylazine combined with ketamine on the dosage of epinephrine required to produce ventricular arrhythmia. Untreated dogs required an arrhythmogenic dose (AD) of 5.88 ± 2.85 μg/kg/min. The AD was 4.28 ± 3.25 μg/kg/min in xylazine-treated dogs, 3.05 ± 2.3 μg/kg/min in ketamine-treated dogs, and 2.96 ± 1.95 μg/kg/min in xylazine/ketamine-treated dogs. The latter two dosages were significantly less than that of the controls (p < 0.025). The duration of increased arrhythmogenicity was also examined. Four hours after drug administration, the AD for xylazine-treated dogs was decreased further to 3.87 ± 2.52 μg/kg/min (p < 0.05). Ketamine-treated dogs had returned partially to normal with an AD of 4.09 ± 3.09 μg/kg/min, as had xylazine/ketamine-treated dogs, at 4.22 ± 2.71 μg/kg/min.