Objectives:To evaluate the effect of treatment with Qishen Yiqi Dripping Pills (芪参益气滴丸, QSYQ) on myocardial injury and myocardial microvascular function in patients undergoing elective percutaneous coronary intervention (PCI).Methods:Eighty patients undergoing elective PCI were randomly assigned to QSYQ and control groups.The QSYQ group received QSYQ at a dosage of 0.5 9 3 times daily (3-7 days before PCI and then daily for 1 month) and regular medication,which comprised of aspirin,clopidogrel,statin,β-blocker,and angiotensin-converting enzyme inhibitor/angiotensin receptor blocker in the absence of contradiction.The control group received only the regular medication.The index of microcirculatory resistance (IMR) was measured at maximal hyperemia after PCI.The fractional flow reserve was measured before and after the procedure.Troponin Ⅰ levels were obtained at baseline and 20-24 h after the procedure.Results:Pre-PCI troponin Ⅰ levels between the two groups were similar (0.028 ± 0.05 vs.0.022 ± 0.04 ng/mL,P=0.55).However,post-PCI troponin Ⅰ levels in the QSYQ group were significantly lower than that in the control group (0.11 ± 0.02 vs.0.16 ± 0.09 ng/mL,P＜0.01).IMR values were significantly lower in the QSYQ group as compared to the control group (16.5± 6.1 vs.31.2 ± 16.0,P＜0.01).Multivariate analysis identified QSYQ treatment as the only independent protective factor against IMR ＞32 (odds ratio=0.29,95％ confidence interval:0.11-0.74,P=0.01).Conclusion:The present study demonstrated the benefit of QSYQ in reducing myocardial injury and preserving microvascular function during elective PCI.