Objectives To investigate the effects of levomepromazine and different desflurane concentrations upon electrocardiographic variables.Animals Twenty adult mongrel dogs of both sexes weighing 6-28 kg.Methods Dogs were divided into two groups of 10 animals. Group I received 1 mg kg(-1) lV of levomepromazine and 15 minutes later anesthesia was induced with propofol (3 mg kg(-1) IV). Desflurane end-tidal concentration was set at 1.6 MAC. After 30 minutes at this concentration, measurements were taken and the end-tidal concentration was reduced to 1.4 MAC. Thereafter, it was reduced to 1.2 and then 1.0 MAC at 1.5-minute intervals. The same procedure was followed for group 2, except that levomepromazine was replaced with 0.2 mL kg(-1) of 0.9% saline solution and more propofol was needed for induction (7 mg kg(-1)). The animals' body temperature was maintained between 38.3 and 39 degreesC using a heating pad. The electrocardiographic tracing was obtained from lead II throughout the experimental period. The measurements were taken immediately before the administration of levomepromazine or placebo (T-1), 15 minutes after pre-medication (T-2) and 30 minutes after the establishment of 1.6 MAC (T-3)The other measurements were made at the concentrations of 1.4, 1.2, and 1.0 MAC, respectively (T4-6). The numerical data were submitted to analysis of variance plus F-test (p < 0.05).Results the dogs that received levomepromazine had a decrease in heart rate. However, in both groups it increased with desflurane administration. Levomepromazine, in association with desflurane, did not induce significant electrocardiographic changes, and all mean values (except P-wave duration) were within the reference range for this species.Conclusions and clinical relevance This study documented that levomepromazine, in association with desflurane, does not induce significant changes in electrocardiographic variables, suggesting that this drug combination has minimal effect on myocardial conduction.