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Background Numerous studies have observed effects of myocardial bridge on myocardial blood flow perfusion and arteriosclerosis from the angle of histology. However, there were few studies concerning ultrastructure characteristics of coronary artery and proximal and distal vascular endothelial cells with the influence of myocardial bridge. Objective To observe myocardial bridge mural coronary artery and proximal endothelial cell ultrastructure characteristics and myocardial bridge-induced hemodynamic changes. Methods Left coronary artery, mural coronary artery proximal end, mural coronary artery and mural coronary artery distal end of 10 patients with coronary artery bypass grafting were treated with heparin-saline and 4% glutaral. The characteristics of vascular endothelial cells and basal lamina were observed with a scanning electron microscope. Results and Conclusion Myocardial bridges of 10 samples located in the middle and proximal anterior descending branch, 2.4-3.6 mm in length. Mural coronary artery proximal portion endothelial cells presented orbicular-ovate. Long axis showed the same direction as blood flow. Many defects were seen on cell surface. Mural coronary artery endothelial cells were long, spindle-shaped, with the consistent direction of long axis and blood flow. Few cells dropped out. Microvillus was observed on endothelial cell surface of two samples, with special bridge-like structure, which was commonly found in one end of cells and connected with consecutive cells following liberation in the lumens. Endothelial cells from mural coronary artery distal end were irregular, with a few detects on the surface, clear boundary, no drop out. Endothelial cells from mural coronary artery had similar area as endothelial cells from the proximal and distal ends. However, perimeter was significantly increased, but morphous index was significantly low (P <; 0.05). These indicated that endothelial cells of the mural coronary artery are free from atheroscle- osis due to higher shear stress caused by myocardial bridge. The intima of the section proximal to mural coronary artery was likely to be sclerosed due to the lower and oscillatory shear force.