Background: Peri-procedural myocardial injury (PMI) is a common complication of percutaneous coronary intervention (PCI), which cannot be entirely avoided using available treatments. The findings of earlier research have shown that Shen-Yuan-Dan (SYD) capsules, a traditional Chinese medicine, can potentially alleviating PMI. This study aimed to confirm further this hypothesis in a rigorous, well-designed randomized controlled study. Methods: Our clinical trial was randomized, double-blinded, and placebo-controlled. A total of 181 patients with unstable angina (UA) undergoing elective PCI were randomized to pretreatment with SYD or a placebo under the basis of conventional treatment; 87 patients were pretreated with SYD (4 capsules, 3 times a day, with a further 4 capsules 2 h before PCI) 3 days before the procedure, and 94 patients were given a placebo. No patients received reloading statins before PCI, and SYD or placebo was maintained for 1 month after PCI. The primary endpoint was the incidence of PMI. The secondary endpoint was calculating the incidence rate of all 30-day major adverse cardiovascular events (all-cause mortality, non-fatal myocardial infarction, unplanned revascularization). The safety outcomes, including abnormalities in electrocardiogram and serum biochemical examinations caused by drug use, were also tested. Results: The levels of creatine kinase-myocardial band (CK-MB) in both the SYD and placebo groups were increased at 4 h and 24 h after PCI compared with before the procedure (P