Background: Coronary slow flow (CSF) is a phenomenon characterized by delayed contrast medium progression in angiography in the absence of obstructive coronary epicardial disease. However, there is currently no definite effective therapy. A small sample self-controlled study had suggested an immediate improvement in coronary slow blood flow by Shexiang Tongxin Dropping Pills (STDP). But high-quality evidences on drug dosage, medication cycle and long-term effects are still lacking while the mechanism of STDP remains unclear. Methods: This study is a randomized, double-blinded, and placebo-controlled clinical trial. A total of 64 CSF patients diagnosed by coronary angiography will be randomly allocated into the test group, using STDP, and the control group, using placebo. The main efficacy indicators for immediate effects include thrombolysis in myocardial infarction (TIMI) blood flow grading and corrected TIMI frame count. Long-term effects will be evaluated by the comparison of cardiac radionuclide score, and patient condition such as angina readmission rate and angina scale. The safety indicators include a routine complete blood count, liver and renal function test, cardiac markers (including TnI, CK-MB, Myo), NT-proBNP, coagulation function, 12-lead electrocardiogram, and echocardiography. All adverse events during the trial will be recorded. Moreover, endothelial factors (including ET-1, NO, eNOS, iNOS), inflammatory factors (including adropin, IL-6, IL-1, IL-18, TNF-α, Lp-PLA2, hs-CRP) will be observed. Blood stasis syndrome (including platelet activation factors such as CD62 and CD63, coagulation function and blood stasis syndrome score) will be evaluated.Trial registration: Chinese Clinical Trial Registry, ChiCTR2000035167. Registered on August 2, 2020. http://www.chictr.org.cn/showproj.aspx?proj=57349
