Atherosclerosis is the most common causes of vascular diseases and it is associated with a restriction in the lumen of blood vessels. So; the study of blood flow in arteries is very important to understand the relation between hemodynamic characteristics of blood flow and the occurrence of atherosclerosis. The practi cal and theoretical investigations of blood flow in the left anterior descending coronary artery (LAD) are achieved in this study.Finding out the appropriate geometrical dimensions for the theoretical simulation is done by analysis data of real patients from coronary angiography as well as estimating of blood velocity from the angiographyscans without having a required data on velocity by using some mathematical equations and physical laws. Fifty-eight patients were included in this study that underwent cardiac catheterization for diagnostic coronary angiography.43 Patients of them (group II) were of more than 25% diameter stenosis in the proximal site of the LAD artery; while the remaining (group I) was ofless than 25% diameter stenosis at the same segment of LAD, under the study, they was considered to be a control group or normal one. It found some information that may explain the ability of small arteries to develop the lesions with time mainly in proximal site of LAD artery. For investigation the fluid-structural response to pulsatile Newtonian and non-Newtonian blood flow through an axisymmetric stenosed coronary artery; the theoretical simulation is built up by using the ANSYS 11, to evaluate the biomechanical parameters in the atherosclerotic process. The flow was set to be laminar. Rigid and Newtonian cases were investigated to provide an understanding on the effects of incorporating the Fluid-Structural Interaction (FSI) into the model. The wall of the vessel was set to have isotropic elastic properties. The wall expansion was found to decrease the axial velocity and increase the recirculation effects of the flow. For validation of the models and methods used, the computation results are compared with the previous studies. The non-Newtonian Carreau model was investigated with FSI, which showed a little difference in comparison with the Newtonian flow model in terms of velocity, pressure, wall shear stress (WSS), and stress distribution.