Acquired von Willebrand syndrome is a disease present in many patients with ventricular assist devices (VAD) which causes dysfunction in the protein von Willebrand factor (vWF). This study shows how shear rates seen in VAD-induced flow can affect platelet adhesion due to platelet dependence on vWF interactions. Shear rate and presence of vWF cleaving protease ADAMTS-13 are shown to have a significant effect on the ability of platelets to adhere to an injury site.