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Introduction: Glycyrrhiza glabra has been traditionally used as a medicinal plant in Iran. In this study to determine some of its mechanisms, the effects of hydro alcoholic extract of Glycyrrhiza glabra on electrocardiogram were examined by the following procedure: methods: Adult male rats were anesthetized via injection of pentobarbital sodium, then Femoral vein and femoral artery were canulated for injection and blood pressure recording respectively. Electrocardiogram was recorded by limb electrodes linked to A-D instrument power lab Bio amplifier also Blood pressure was recorded by pressure transducer linked to A-D instrument power lab.Tested groups were as follows: The first group, received Glycyrrhiza glabra extract (90mg/kg) and equivalent volume of the Glycyrrhiza glabra solvent (ethanol %70). the second group, received Glycyrrhiza glabra extract and acetylcholine (.01 mg/kg). Result: The result showed a significant decrease of RR interval and R amplitude in presence of licorice extract, licorice extract and acetyl choline with comparing to control condition also systolic and diastolic blood pressure showed a significant decreasing in presence of licorice extract with comparing to control condition. Conclusion: It can be concluded that Glycyrrhiza glabra has a positive chronotropic and negative ionotropic effects on heart via synergistic effect with cholinergic system