Background:Coronary blood flow reserve (CFR) is a useful method for evaluating the functions of microvessels in patients with chest pain but normal coronary angiogram, and impairment of CFR have been shown to be early manifestations of atherosclerosis and coronary artery disease(CAD).Recently, Osteoprotegerin (OPG) has been suggested to have an important role in atherosclerosis and coronary artery disease(CAD). We therefore hypothesized that circulating levels of OPG would predict microcirculatory dysfunction in patient with chest pain but normal coronary angiogram . Methods: We studied 72 subjects (M/F=37:35, mean age 56짹9 years) with chest pain and normal coronary angiogram. CFR was estimated with TTE and dipyridamole. Patients with history of myocardial infarction ,atrial fibrillation, structural valve disease, or more than mild functional mitral regurgitation and interventricular septal or posterior wall thickness more than 12 mm were excluded from this study.Serum OPG levels were measured by enzyme-linked immunoassay. Results:The CFR of hypertensive patients(2.43짹0.69,n=42) was non significantly decreased compared with that of normotensive subjects(2.46짹0.89,n=30).CFR showed no correlation with OPG.(r=-0.05,p=0.67)However,a marked interaction between hypertension and OPG was seen for low CFR(<1.9) (P for interaction=0.082, table). Conclusion:Independent and significant association of between high OPG and hypertension was notably noted in impairment of CFR in patients with chest pain and normal coronary angiogram.