CD40 ligand (CD154)-induced ultra-large von Willebrand factor (vWF) multimer-mediated endothelial cellplatelet-monocyte interaction may play an important role in adaptive and maladaptive vascular remodeling processes. Here we analyzed the impact of and conditions favouring the deposition of these multimers on the endothelial cell (EC) surface by way of CD40-CD154 co-stimulation in settings mimicking different forms of blood flow. Upon exposure to low oscillatory shear stress and sCD154, a release of vWF multimers comparable to histamine stimulation was monitored on the EC surface in a string-like fashion. Moreover, ex vivo perfused carotid arteries of wild type mice at low laminar shear stress rates showed a luminal release of vWF as ultra-large vWF multimers (ULVWF) upon stimulation with sCD154 which was absent in blood vessels of CD40 knockout mice. The observed CD40- and flow-dependent vWF release from intact endothelial cells and subsequent vWF multimer formation may facilitate adhesion and subsequent activation of circulating platelets at atherosclerotic predilection sites, which are characterized by disturbed flow patterns. This in turn may amplify endothelial cell-monocyte interaction, thus possibly initiating or promoting early atherosclerotic lesion formation.