Objective： To observe abnormalities in heart rate variability （HRV） in diabetic rats and to explore the effects of treatment with Guizhi Decoction （桂枝汤） on cardiac autonomic nervous （CAN） imbalance. Methods： A radio-telemetry system for monitoring physiological parameters was implanted into rats to record electrocardiac signals and all indictors of HRV [time domain measures： standard deviation of all RR intervals in 24 h （SDNN）, root mean square of successive differences （RMSSD）, percentage of differences between adjacent RR intervals greater than 50 ms （PNN50）, and standard deviation of the averages of RR intervals （SDANN）; frequency domain measures： low frequency （LF）, high frequency （HF）, total power （TP）, and LF/HF ratio]. The normal group was randomly selected, and the remaining rats were used to establish streptozocin （STZ）-induced diabetic model. After 4 weeks, the model rats were divided into the model group, the methycobal group, and the Guizhi Decoction group, 9 rats in each group. Four weeks after intragastric administration of the corresponding drugs, the right atria of the rats were collected for immunohistochemical staining of tyrosine hydroxylase （TH） and choline acetyltransferase （CHAT） to observe the distribution of the sympathetic and vagus nerves in the right atrium. The myocardial homogenate from the interventricular septum and the left ventricle was used for determination of TH, CHAT, growth-associated protein 43 （GAP-43）, nerve growth factor （NGF）, and ciliary neurotrophic factor （CNTF） levels using an enzyme-linked immunosorbent assay. Results： （1） STZ rats had elevated blood glucose levels, reduced body weight, and decreased heart rate; there was no difference between the model group and the drug treated groups. （2） Compared with the model group, only RMSSD and TP increased in the methycobal group significantly （P〈0.05）; SDNN, RMSSD, PNN50, LF, HF, and TP increased, LF/HF decreased （P〈0.05）,
