Purpose: To study the effect of dexmedetomidine (Dex) on myocardial ischemia-reperfusion injury (MIRI), and the associated mechanism of action.Methods: Sixty Sprague-Dawley (SD) rats were assigned to sham, ischemia-reperfusion (I/R), Dex, and MD groups (methyllycaconitine prior to injection with Dex), with 15 rats in each group. Pathological changes in myocardial tissues were determined in all groups. Protein expression levels of HMGB1, TLR4, NF-κB and myeloid differentiation protein 88 (MyD88) in serum and myocardial tissues were assayed and compared.Results: Protein levels of HMGB1, TLR4, MyD88 and NF-κB were significantly higher in heart muscle I/R rats than those in sham group, but lower in heart muscle of rats in Dex group than in heart muscle of I/R rats (p < 0.05). However, they were significantly up-regulated in MD group, relative to Dex group (p< 0.05).Conclusion: Dex exerts a protective effect against ischemia/reperfusion-induced myocardial damage via HMGB1-TLR4-NF-κB signal axis via CAP, and thus, is a potential agent for the management of myocardial disease.