Background: Myocardial bridging (MB) is defined as a segment of a major epicardial coronary artery that traverse intramurally through the myocardium beneath the muscle the bridge. We investigated whether the MB length can impact on the length and distribution of acetylcholine (Ach)-induced endothelial dysfunction and the ischemic clinical manifestation.Methods: A total 899 patients (pts; 556 men, Mean Age; 56.58짹11 years) with typical or atypical anginal symptoms underwent diagnostic coronary angiography (CAG) and Ach provocation test. Among them, 163 pts with typical MB on CAG were divided into two groups. The Focal MB group (n=84) was defined as the length of MB segment < 20mm, The Diffuse MB group (n=79) is ��� 20mm. We compared the characteristics of Ach-induced endothelial dysfunction and the ischemic clinical manifestations between the two groups. Results: Baseline characteristics and coronary risk factors were similar between the two groups. A total 112 pts out of 163 pts (68 %) with MB showed significant Ach-induced endothelial dysfunction. MBs were observed mostly in mid left anterior descending artery (LAD) in right anterior oblique view. Unsurprisingly, the length of MB segment was not related to the length and the location of Ach-induced endothelial dysfunction, ECG change (ST elevation or depression) and the severity of chest pain during the Ach provocation test (Table). Conclusion: When we categorized all MB pts into two different groups according to the MB length, it was not associated with the length and location of endothelial dysfunction and the ischemic clinical manifestations. Ach-induced coronary artery endothelial dysfunction was significantly associated with the presence of MB itself but was not closely related to the length of MB segment whether it was focal or diffuse.