Objective To explore the effect of Tian Xiang Dan（天香丹） on coronary microcirculation dysfunction（CMD） and its possible mechanism. Methods Sixty-three SD rats were randomly divided into a blank control group

a sham operation group

a model group

a nicorandil group and Tian Xiang Dan low

medium and high dose groups

with nine rats in each group. The model of CMD was established in all rats except for the blank control group

by injecting normal saline（for sham operation group） or sodium laurate（for other groups） into the left ventricle after thoracotomy. After modeling

Tian Xiang Dan at a dosage of 0.1188 g/（kg·d）

0.2376 g/（kg·d）

and 0.4752 g/（kg·d） was administered by gavage in Tian Xiang Dan low

medium and high dose groups

respectively; 0.297 mg/（kg·d） nicorandil powder by gavage was administered in nicorandil group; the blank control group

the sham operation group

and the model group were given 2 mL normal saline by gavage; all administrations were performed once per day

for 28 days. Cardiac function was detected in all the rats. Hematoxylin and eosin（HE） stain and martius yellow-acid fuchsin-aniline blue stain were used to observe the pathological changes in the capillary blood vessels of coronary circulation. The ultrastructure of the myocardial tissues was investigated; the expression of nuclear factor erythroid 2-related factor 2（Nrf2）/antioxidant response element（ARE） signaling pathway proteins

including Nrf2

Kelch-like epichlorohydrin-associated protein 1（Keap1）

quinone oxidoreductase 1（NQO1）

catalase（CAT）

heme oxygenase-1（HO-1） were determined. Results In model group

there was thromboembolism in capillary blood vessels; myocardial cells showed fibrosis; and microthrombosis was severe

while in other treatment groups

the degree of thrombosis was light with only few microthrombi. Compared to the blank control group

the cardiac function in sham operation group and model group decreased significantly（P<0.05）

while no significant differences were found between groups in the expression of Nrf2

Keap1

NQO1

CAT and HO-1（P>0.05）. Compared to the model group

the cardiac function significantly improved in nicorandil group and Tian Xiang Dan medium and high dose groups（P<0.05）; and the expression levels of Nrf2

NQO1

CAT

and HO-1 proteins significantly increased in Tian Xiang Dan medium and high dose groups（P<0.05）. Compared to nicorandil group

there was higher expression levels of Nrf2

NQO1

CAT proteins in Tian Xiang Dan medium group

and higher expression level of HO-1 protein in Tian Xiang Dan high group（P<0.05）. Conclusion Tian Xiang Dan can alleviate microthrombosis and mitochondrial damage

thereby improving coronary microcirculation dysfunction. The underlying mechanism may be related to Nrf2/ARE signaling pathway through which oxidative stress is reduced.