Objectives: The cardiac side effect of 5-hydroxytryptamine-3 receptor antagonists (5-HT3-RA) is an area under active investigation, and granisetron hydrochloride, an agent of this class, is currently under development for multiple therapeutic indications such oncology and parvoviral gastroenteritis induced acute vomiting in dogs. This study was performed to assess the electrocardiographic (ECG) effects of slow-single intravenous dose of granisetron. Materials and Methods: Sixteen adult, crossbreed, female clinically healthy (Body weight: 23.32±0.78 kg) were used in this study, then they randomly divided into two groups. The electrocardiogram tracings were taken immediately before and repeated at 5,15,30,60,120 minutes and 6 and 12 hours after 0.5 mg/kg granisetron similar to placebo in control groups. Heart rate and electrocardiographic parameters (PR intervals, QRS duration, ST-segment, T-wave amplitudes, QT, JT, QTc and JTc intervals were evaluated in Lead II. Results & Conclusion: Data were analyzed using an analysis of comparison of means for the treatment groups compared to the control group using repeated measurement T-test at the P<0.05 by SPSS 19.0. In comparison of parameters in two groups, they were significantly unchanged, but the results in treatment group related to before injection of granisetron (T0), by the analysis using paired t-test (p≤0.05) revealed a significant but clinically asymptomatic and transient PR, QRS, QT, JT, QTc prolongation and a decrease in HR. Key Words:

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