Objective: To investigate the mechanism of protective effect of Astragalus (As) plus ligustrazine (Lt) against myocardial ischemia reperfusion injury (MIRI) during open heart surgery of cardiopulmonary bypass

and the treating principle of MIRI in TCM.Methods: Twenty-four patients were randomly divided into three treated groups and treated with As injection

Lt injection and both (As + Lt) respectively

6 in each group

and the remainder 6 were taken as control group. Blood samples of them were collected before anesthesia (T1)

10 minutes after occlusion of aorta (T2)

10 minutes(T3) and 30 minutes(T4) after the release

and end of operation (about 180 minutes after release

T5) respectively to test the levels of aspartate aminotransferase ( AST )

lactate dehydrogenase (LDH)

creatine kinase (CK)

MB isoenzyme of CK (CK-MB)

malondialdehyde (MDA) and the activity of Superoxide dismutase ( SOD )

nitric oxide ( NO )

nitric oxide synthetase (NOS).Results: The levels of AST

LDH

CK were reduced in the treated groups

showing significant difference (P< 0.05 or P < 0. 01 ) as compared with those in the control groups. Among them the effect in the AS + Lt group was the best. And NO activity in As group at T5 and As + Lt group at T4

T5 was higher than that in the control group.Conclusion : The mechanism of MIRI is Qi deficiency and blood stasis in TCM

its treating principles should be promoting Qi and removing blood stasis. According to the authors’ study

combined As + Lt therapy is more effective in protecting against MIRI than that using the 2 medicines separately.