FXI inhibition limits vascular graft-associated platelet deposition under high arterial shear. Effects of FXI inhibition or ASA administration on platelet deposition on collagen-coated (2-mm id) vascular grafts are shown. Collagen-coated vascular graft segments were placed in permanent arteriovenous shunts in untreated (n = 9), ASA-treated (n = 6), and aXIMab-treated (n = 5) animals. Blood was allowed to flow through the grafts at a rate of 100 mL/min, producing an average initial wall shear rate of 2120 s⁻¹. The flow was maintained by the pulsatile arterial pressure until the graft occluded (defined as ≤ 20 mL/min flow rate). Thrombi that formed in the grafts in the aXIMab-treated animals were unstable, embolized more frequently than in ASA-treated animals, and did not occlude the grafts for at least 60 minutes. Significance levels (*P = .05; **P < .01) pertain to comparisons with untreated controls, using the log-rank test, with the nonoccluded devices being censored. Values are means plus or minus SEM.