Objective To determine the effect of trimetazidine on myocardial injury related to percutaneous coronary intervention (PCI) and postoperative left ventricular function in the patients with unstable angina pectoris (UAP). Methods A total of 106 UAP patients undergoing selective PCI in our department from January 2011 to January 2014 were prospectively enrolled in this study. They were randomly assigned into trimetazidine group (n＝51) and control group (n＝55). The patients from the former group, besides conventional drug treatment, were given oral administration of 60 mg trimetazidine in 0.5?1.0h before PCI, and of 20mg, 3 times/d after the surgery. The serum concentration of cardiac troponin I (cTnI) was measured before and in 16?18h after PCI. Telephone follow-up was carried out to investigate PCI-related changes. Results The serum cTnI level was significantly higher in 16?18h after than before PCI in the both groups (P＜0.05), with that of the trimetazidine group elevated more significantly (P＜0.05). The percentage of the patients with the post-operative cTnI level ＞0.10μg/L was obviously smaller in the trimetazidine group than in the control group (P＜0.05). Till the end of 12 months’ follow-up, the trimetazidine group had significantly lower left ventricular end systolic dimension [(31.00±4.33) vs (33.29±2.11)mm, P＜0.05)], and obviously higher left ventricular ejection fraction [(65.65±3.94)% vs (62.29±3.06)%, P＜0.01] than the control group, but there was no difference in the incidence of major adverse cardiac event (MACE) between the 2 groups (7.8% vs 9.1%). Conclusion Pre-operative administration of trimetazidine reduces the PCI-related myocardial injury, and long-term post-operative treatment improves left ventricular function in patients with UAP.