Objective: The relationship between myocardial bridging (MB) and ischemic heart disease is still controversial. In this study, we aimed to evaluate the existing atherosclerosis and noninvasive endothelial function of brachial artery in patients with MB. Methods: The present study included 50 patients (group I) who had MB in left anterior descending (LAD) on coronary angiography. All of the coronary artery segments were evaluated by intravascular ultrasound (IVUS). Endothelial function was assessed with measurement of flow-mediated dilatation (FMD) and nitrate-dependent dilatation in the brachial artery. The study also included 30 healthy control subjects (group II). Patients in the group I were further subdivided into two subgroups based on the findings on IVUS: group IA included 20 patients without atherosclerotic lesions and group IB included 30 patients with atherosclerotic coronary artery disease in addition to MB. Results: FMD values were found to be significantly lower in the patients with MB (group I) than in the control (6.4 +/- 3% vs 11 +/- 4%, P < 0.001). In regard to FMD values in subgroups, FMD was 7 +/- 2% in the group IA and 5.8 +/- 1% in the group IB (P = 0.023). On IVUS, atherosclerotic plaque was found proximal to the bridge in the same coronary artery segment in addition to MB in 75% of the patients in group I (group IB). No atherosclerotic plaque was found in within or distal segments of MB. Conclusion: Endothelial function is impaired in patients with MB and there is an increased tendency for atherosclerosis proximal to the bridge in the patients with MB. Endothelial dysfunction is more severe in the patients with atherosclerosis proximal to the bridge.