Introduction During the cardiac cycle, coronary flow is uniquely developed significantly on diastolic phase. And there are so many braches and curved area human circulatory system. These areas are known to be atherosclerosis-prone area. So, the understanding the flow dynamics in these areas is important to study the atherogenesis. The blood viscosity is known to do non-Newtonian flow behavior with viscosity values decreasing as shear rate increases. The blood viscosity of atherosclerotic patients is demonstrated significantly elevated values at almost all shear area, when compared to the control samples according as severity of unstable acute ischemic events. Among the patients, patients with acute coronary syndrome demonstrated significantly higher viscosity than patient with stable angina. This study was aimed to find the particle movement pattern in coronary bifurcation model in various situation of blood viscosity. Method Left main coronary arterial model was made by digital subtraction and novel 3D reconstruction methods analyzed from coronary angiography data base. Inlet flow velocity waveform of the pulsatile flow obtained from in vivo intravascular Doppler ultrasound flow data. In vivo pressure profile was adopted also. For attaining effective numerical analysis of hemodynamics, we used finite volume method, adapting Rhie-Chow algorithm. The governing equations are calculated under a non-staggered grid system. We calculated all the profile of flow patterns, wall shear stress, and particle residence time during one cardiac cycle according as varying blood viscosity. Considering the design of micro-robot for interventional usage of coronary aterial disease, it is essential to understand the flow dynamics in coronary arterial trees. Result During the cardiac cycle, coronary flow phases are classified as accelerated and decelerated phase. The flow separation and secondary flow around the bifurcation area is more significant on deceleration phase. The profiles of wall shear stress are more separated on deceleration phase, also. And these patterns are more prominent when the blood viscosity is increased. Furthermore, higher blood viscosity, more increased the particle residence time