The vascular system is lined by a continuous monolayer of endothelial cells. Located between the circulating blood elements and surrounding tissues, these cells provide a non-adherent and non-thrombogenic surface, and help maintain blood flow and vascular reactivity. These cells also have the capacity to regulate cell migration and proliferation. Multiplicity of endothelial function is mediated by their ability to elaborate regulatory molecules such as anticoagulants, prothrombotic mediators, vasodilators, vasoconstrictors, growth factors, cytokines, adhesion molecules and extracellular matrix components. The integrity of the endothelium is therefore, a fundamental requirement for the maintenance of normal structure and function of the vessel wall.