[ ABSTRACT] AIM:To investigate the preventive effect of Guizhi decoction on myocardial injury after chemical sympathectomy induced by 6-hydroxydopamine (6-OHDA).METHODS:Wistar rats (n=54) were randomly divided in-to 6 groups.Methycobal and Guizhi decoction ( with different proportions between Ramulus Cinnamomi and Radix paeoniae Alba at 2∶1, 1∶2 or 1∶1) were pre-administered to the rats.Immunohistochemical method was used to observe the cardiac sympathetic nerve distribution.The contents of tyrosine hydroxylase (TH), choline acetylaminotransferase (ChAT) and growth-associated protein 43 (GAP-43) in the left ventricle were measured by ELISA.The serum levels of myocardial en-zymes and morphology of myocardial tissues were also observed.RESULTS:6-OHDA successfully induced cardiac sympa-thetic denervation as the contents of TH and GAP-43 in the left ventricle declined significantly.Compared with model group, the content of TH was elevated in both methycobal group and Guizhi decoction groups, while the content of GAP-43 was elevated only in Guizhi decoction groups.The serum levels of myocardial enzymes and the histopathological changes of the cardiac tissues were deteriorated after injection of 6-OHDA, indicating that the myocardial injury was established. Methycobal and Guizhi decoction normalized the abnormal change.Guizhi decoctions at 2∶1 and 1∶1 showed the best effi-cacy.CONCLUSION:6-OHDA-induced sympathetic denervation causes myocardial injury.Guizhi decoction with the proportions between Ranulus Cinnamomi and Radix paeoniae Alba at 2∶1 and 1∶1 effectively alleviate the myocardial injury after cardiac sympathetic denervation induced by 6-OHDA.