AIM: To investigate the effects of Qidantongmai tablet (QDTMT) on the equilibrium between ET and NO and the equilibrium between TXB 2 and 6 keto PGF 1α in the canine model of myocardial ischemia reperfusion injury (MIRI). METHODS: Twenty four adult healthy cross bred canines were randomly assigned to four groups: Control group, ischemia preconditioning group, QDTMT low dosage group (QDTMTL) and QDTMT high dosage group (QDTMTH). Canines in all groups took QDTMT (or NS) orally for a week under the same condition. The model of MIRI was established by ligating levo anterior descending branch of coronary artery. The contents of ET, NO, TXB 2 and 6 keto PGF 1α in plasma were measured at four time points: Pre drug (T 1), 20 min after ligation (T 2), 10 min (T 3) and 30 min (T 4) after reperfusion respectively and the equilibrium between NO / ET and that between 6 keto PGF 1α / TXB2 were analyzed. RESULTS: Compared with the control group, QDTMTL and QDTMTH reduced the level of ET and TXB 2, promoted the expression level of NO, increased the activity of 6 keto PGF 1α , and regulated the equilibrium between NO and ET and that between 6 keto PGF 1α and TXB 2 ( P<0.05, P <0.01). There is no significant difference between QDTMT groups and the ischemia preconditioning group( P >0.05). CONCLUSION: Just as ischemia preconditioning, QDTMT has good protective effects on MIRI. The mechanism of protection relates to its function of decreasing the level of ET and TXB 2, promoting the expression level of No, increasing the activity of 6 keto PGF 1α , and regulating the equilibrium between NO and ET and the equilibrium between 6 keto PGF 1α and TXB 2.