Background: The relationship between baseline coronary artery fixed stenosis measured by quantative coronary angiogram (QCA) and acetylcholine (Ach)-induced endothelial dysfunction has not been clarified in detail. We investigated whether baseline coronary artery fixed lesion can impact on acetylcholine (Ach)-induced endothelial dysfunction. Methods: A total 274 patients (pts) without previous cardiovascular disease and conventional coronary risk factors such as diabetes, hyperlipidemia, or hypertension underwent diagnostic coronary angiography (CAG) with Ach provocation test. Patients were divided into two groups according to presence of baseline coronary fixed lesion (<50%). We compared the characteristics of Ach-induced endothelial dysfunction and the ischemic clinical manifestations between the two groups. In addition, we analyzed the impact of baseline coronary artery fixed stenosis and other conventional risk factors on Ach-induced endothelial dysfunction. Results: Baseline characteristics were similar between the two groups. The group with baseline fixed lesion showed more frequent, severe Ach-induced endothelial dysfunction (Table). There were more pronounced narrowing at baseline non-stenotic area than the stenotic area (75.06짹15.23, 45.75짹19.53, p<0.001). In multivariate analysis, baseline coronary fixed stenosis and age were significantly associated with Ach-induced endothelial dysfunction (OR 15.6, P<0.001). Conclusion: Baseline coronary fixed stenosis was strongly associated with more frequent and severe Ach-induced endothelial dysfunction. Significant Ach-induced endothelial dysfunction was more profound in non-stenotic area compared with that of stenotic area.