Objective To observe the curative effect of Didang Decoction and its disassembled formula on myocardial lesion in diabetic rats. Methods Totally 105 SD rats were injected streptozotocin solution intraperitoneally with 55 mg / kg to prepare the diabetic rat model

100 rats of successful model were randomly divided into model group

Didang Decoction group

Taoren（ Semen Pruni persicae） Dahuang（ Radix Rumici Japonici） group

Shuizhi（ Leech） Mangchong（ Tabanus） group and valsartan group

with 20 in each group. The other 10 normal SD rats served as the control group. Didang Decoction group

Shuizhi Mangchong group and Taoren Dahuang group gavage corresponding Chinese medicine 10 g /（ kg·d）

valsartan group gavage valsartan capsule 80 mg /（ kg·d）

the control group and the model group were perfused with distilled water

1 time a day. After 8 weeks

HE staining in left ventricular myocardium tissue of the rats in each group would be observed under light microscope; the changes of myocardial fibrosis are observed by Masson staining

and the collagen area of myocardium is calculated; ultrastructure changes of myocardial cells are observed by electron microscope. Results The results of HE staining showe that the left ventricular myocardial cells in the model group are enlarged and arranges in disorder

and there is inflammatory cells infiltration; The arrangement of myocardial cells in the Didang Decoction group and valsartan group is relatively neat

the intercellular space is decreased

interstitial and perivascular extracellular matrix is decreased. Compared with the control group

the ratio of the collagen area to the total area of myocardium in the model group is increased（ P < 0. 01）; The ratio of the collagen area to the total area in the Didang Decoction group is significantly decreased than that in the model group（ P < 0. 01）

however it is of no significant change in the Taoren Dahuang group and Shuizhi Mangchong group（ P > 0. 05）. The results of electron microscopy observation of myocardial ultrastructure are as follows: In the model group

the myocomma showes blurred

myofibrillar dissolves

or even disappears; In the Didang Decoction group and valsartan group

the myocomma showes neat

the mitochondrial morphology is oval and the structure is roughly normal. Conclusion Didang Decoction can improve the pathological degree of myocardial fibrosis in diabetic rats

which can have preventive and therapeutic effect against diabetic cardiomyopathy.