Activation-independent and shear rate-dependent aggregation and disaggregation of platelets perfused over immobilized VWF. Whole blood containing 93 μM PPACK as the anticoagulant, 10 μM PG E₁ to block platelet activation, and 10 μM mepacrine to render platelets fluorescent for visualization, was perfused over a surface coated with immobilized VWF. The images shown are single frames from a real-time recording (Video S1). A timeline (black horizontal bar) indicates at what moment during the perfusion experiment a given image was taken, as shown by the position of the corresponding letter (A, 55 seconds; B, 130 seconds; and C, 380 seconds).Avertical white bar separates the timeline in segments corresponding to periods of perfusion at different wall shear rates (5500 or 13 000 s^-1). The images are representative of 3 separate experiments performed with blood from different donors.