This document discusses the role of CD40 and its ligand CD40L in atherosclerosis and thrombosis. It reports that CD40L plays an important role in inflammation, atherosclerotic plaque progression, thrombosis, and restenosis. CD40L is expressed on platelets, B cells, and T cells and triggers predominantly Th1 cytokine-driven inflammation during atherogenesis. Studies show that CD40L activation inhibits endothelial cell migration, potentially contributing to increased risk of acute coronary events by reducing re-endothelialization after plaque injury. High levels of circulating CD40L may be associated with increased cardiovascular risk.