The onset of coronary heart disease may be governed by distribution and magnitude of hemodynamic shear stress in the coronary arteries. This study numerically examines pulsatile blood flow through the left coronary artery system. A triphasic waveform is employed to simulate pulsating flow. Five non-Newtonian models, as well as the usual Newtonian model, are used to describe the viscous shear-thinning behavior of blood. It is concluded that when using computational fluid dynamics (CFD) to numerically investigate blood velocity profiles within small arteries, such the coronary artery system examined in this work, great care should be taken in choosing a blood viscosity model. It is suggested that the generalized power law model be the viscous shear thinning model of choice. When using CFD to investigate only patterns of wall shear stresses, the model selection is not as crucial and the simple Newtonian model will suffice but when the magnitude of WSS is of great importance, as in the case of the determining the development of coronary artery disease, the model selection is key.