Background : The evidence of relationship between coronary spasm and myocardial bridging is lacking. Chronic vascular injury in bridging segment may induce endothelial damage. Therefore, we investigate to determine whether myocardial bridging increases the risk of coronary spasm via endothelial dysfunction. Method : In 72 consecutive patients with chest pain but no atherosclerotic coronary lesion confirmed by coronary angiography, a spasm provocation test was performed by infusing acetylcholine (Ach), endothelial dependent vasodilator, into the left coronary artery. Provocation test was defined as positive when the diameter of the coronary artery was reduced by 50 % and there was ST segment changes with chest pain. Result : In 22 patients (male 15, 58.2짹6 years old), myocardial bridging was identified (defined as > 15 % reduction in the diameter of the coronary artery in systole). 50 patients without bridging were considered control (male 38, 54.3짹4 years old). All bridgings were located in mid LAD. Spasm was documented in 17 of 22 patients with bridging and in 12 of 50 patients in control group (77.2 % vs. 24.0 %, p < 0.001). In bridging group, spasm was induced dominantly in bridging site of mid LAD in 14 patients (82.3 %) rather than proximal LAD in 2 patients (11.7 %) or mid LCX in 1 patient (5.8 %). There were no significant differences in Ach dose of inducing spasm and QCA parameters between two groups. Conclusion : Myocardial bridging increase the risk of coronary spasm via endothelial dysfunction in bridging segment. We suggest that spasm provocation test should be considered in all patients with chest pain, who have documented myocardial bridging on coronary angiography, to exclude the spasm as origin of chest pain.