Abstract: Background Imidazoline receptors are important targets of anti-hypertension drug. Although previous studies indicated that agmatine（Agm） is probable the endogenous ligand of imidazoline receptor,the central cardiovascular effects and mechanisms of the Agm were not clear. Objective To study the cardiovascular effects of Agm by injection of Agm into the lateral cerebral ventricle（ICV） in anesthetic rats and investigate its cardiovascular mechanisms by pre-application idazoxan,MK-801 or clonidine（Clo）. Methods In seventy anesthetized,spontaneously respired male SD rats,twenty-nine rats were randomized to receive following approaches:control,Agm 5,10,20 μmol and Clo 1.0 μmol injected into ICV to observe their central cardiovascular effects. Another forty one rats were pre-treated with idazoxan,MK-801,Clo,or aCSF and blood pressure（BP） and heart rate （HR） changes by 10 μmol Agm or Clo were investigated. Results ICV of Agm 5 μmol mean blood pressure（MBP）:（113±5） vs （105±13） mmHg or 10 μmol （103±7） vs （72±9）mmHg（all P＜0.05） induced significantly decreased in BP and HR in anesthetized rats,analogue to the effect by ICV Clo Clo 1.0 μmol,MBP:（92±8） vs （78±19）mmHg,P＜0.05. The cardiovascular functions of ICV Agm were significantly attenuated by pretreatment with central application of imidazoline receptor antagonist idazoxan,NMDA receptor antagonist MK-801 and were almost completely abolished by pretreatment with central application of Clo. Conclusion The bradycadia and hypotension of central Agm are the results of excitation of imidazoline receptors,which were mediated by NMDA receptors. Clo effectively abolish the central cardiovascular effect of Agm.