The use of continuous analgesic infusions (IACs) is an effective strategy for the control of postoperative pain in canines; however, depending on the used drug, cardiac electrophysiology can be altered by the presence of tachyarrhythmias, bradyarrhythmias, ventricular complexes, fibrillation or atrioventricular block. The aim of this study was to evaluate the heart rate and to characterize the electrocardiographic abnormalities during the use of continuous postoperative analgesic infusions of tramadol or lidocaine in ovariohysterectomized bitches using 24-hour Holter monitoring. For this purpose, 26 healthy canine females (26.6 ± 17.6 months, 15.34 ± 7.81 kg) were divided into three groups: Group 1 NaCl 0.9% as control (n = 7), Group 2 lidocaine 100μg / kg / minute (n = 10) and Group 3 tramadol 22μg / kg / minute (n = 9). As results the mean, minimum and maximum heart rate found in each group were Control 100, 40 and 253 bpm. Lidocaine 93, 42 and 238 bpm and Tramadol 90, 43 and 253 bpm; on the other hand, a total of 20/26 (76.9%) of the studied animals presented several electrocardiographic alterations that included in their order SVPC, AVB, VPC and RR pauses, however, there were no statistically significant differences (p<0.05) between the evaluated groups. It is concluded that the IACs of tramadol or lidocaine under the described experimental conditions do not generate statistically significant electrocardiographic alterations, but could play a role in the minimization of those parameters when used in a complementary way during the postoperative period.