Seventy seven adult large mixed breed dogs of either sex were included in this study. The animals were randomly divided into four groups and received the following drug combinations intramuscularly: Group 1 xylazine (0.5 mg/kg) and acepromazine (0.05 mg/kg), Group 2 xylazine (0.8 mg/kg) and acepromazine (0.03 mg/kg), Group 3 xylazine (0.3 mg/kg) and acepromazine (0.08 mg/kg) and Group 4 xylazine (0.5 mg/kg) acepromazine (0.05 mg/kg) and atropine (0.04 mg/kg). Results showed no significant differences in the Pwave and QRS complex durations, PR interval and R waves among the 4 groups. QT interval significantly decreased following drug administration in group 4 compared to groups 1 (P = 0.03) and 3 (P = 0.004). There were significant increases in the QT interval in groups 1 (P = 0.001) and 3 (P = 0.01) after drug injections. Heart rate (HR) significantly decreased in groups 1, 2 and 3 after drug injections (P = 0.004, 0.01 and 0.03, respectively). There was a significant negative correlation between HR, PR and QT intervals, and a positive correlation between HR and P-wave amplitude. There were no significant differences between all groups in the incidence of first and second degree AV blocks.

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