Many studies link hyperviscosity to cardiovascular diseases, hypertension and cerebral infraction, rendering the study of hemodynamic factors very important for understanding, predicting and treating this type of disorders. In this work the effect of blood viscosity on several hemodynamic factors, such as wall shear stress (WSS), wall shear stress gradient (WSSG), blood flow rate and pressure drop in a small-caliber bifurcated artery (parent: 600 mu m, daughters: 470 mu m) was numerically studied. A CFD code, validated by relevant experimental data acquired in this Lab, was used for the simulations. In order to simulate the pulsatile flow of blood a velocity fluctuation has been imposed (U-mean=0.080-0.105 m/s) as inlet boundary condition. As blood is a non-Newtonian fluid, its viscosity was calculated using the Casson model. The results showed that, when blood viscosity increases, the heart must also increase its pumping power (up to 126%) in order to keep cardiac output unchanged. On the other hand, and if it is assumed that the pumping power of the heart is fixed, the blood flow rate is attenuated accordingly (by 64% for the highest hematocrit studied). For all cases studied it was found that at the outer wall of the bifurcation WSS values are lower than those on the rest of the arterial wall. The high WSS and WSSG values calculated at the apex of the bifurcation (10 Pa and 4 x 10(4) Pa/m, respectively, for H-t=45%) indicate that this location is predisposed to endothelium damages. These findings could aid in the comprehension of the mechanisms related to vascular damages caused by hyperviscosity. (C) 2011 Elsevier Ltd. All rights reserved.