Abstract: OBJECTIVE To discuss the effects of different doses of dexmedetomidine (Dex) on myocardial oxidative stress and hemodynamics in patients undergoing heart valve surgery. METHODS A total of 143 adult cases undergoing cardiac surgery because of heart valve disease were selected as research object and divided into control group (n=45), low-dose Dex group (low-dose group, n=50) and high-dose Dex group (high-dose group, n=48) randomly. All patients were given intravenous anesthesia and conventional anesthetic after intubation. And on this basis the patients of low-dose group and high-dose group were given Dex at 0.3 μg·kg^-1·h^-1 and 0.6 μg·kg^-1·h^-1 by pumping persistently while the patients of control group were given same dosege normal saline. To test the levels of superoxide dismutase (SOD), malondialdehyde (MDA) and malondialdehyde (cTnI) in peripheral blood at timing of before cardiopulmonary bypass (T₀), the end of surgery (T₁), 6 h after surgery (T₆), 12 h after surgery (T₁₂) and 24 h after surgery (T₂₄) and record the heart rate (HR), mean arterial pressure (MAP) and cardiac index (CI). The differences in the three groups were compared and their clinical significance was analyzed. RESULTS The levels of cTnI significantly increased in all groups after operation, the increase of the high-dose group was the lowest in three groups, followed by the low-dose group and the control group. There were statistical significance about cTnI at different timing in three groups (all P<0.05). The levels of SOD decreased gradually after operation and the decrease of the high-dose group was the lowest in three groups, followed by the low-dose group and the control group. There were statistical significance about SOD at different timing in three groups (all P<0.05). The changes of MDA took on opposite trend compared with SOD, the increase of the high-dose group was the lowest in three groups, followed by the low-dose group and the control group. There were statistical significance about SOD at different timing in three groups (all P<0.05). The HR and MAP decreased gradually after operation and the CI increased, while there were no statistical significance among three groups. CONCLUSION The dexmedetomidine can significantly reduce the oxidative stress of myocardial cells after cardiac surgery and play a protective role in protecting myocardium. It presents a significant quantitative relationship and there is no obvious adverse effect on hemodynamics, it is worth popularizing and applying in clinic.