 Endothelial cells line the internal lumen of all the vasculature and serve as an interface between circulating blood and vascular smooth muscle cells VSMCs. Apart from being the key participant during the process of angiogenesis, these dynamic structures can actively regulate basal vascular tone and vascular reactivity in physiological and pathological conditions. They respond to mechanical forces and neurohumoral mediators by releasing a variety of relaxing and contracting factors such as nitric oxide NO and prostacyclin. The balance between the vasodilatation and vasoconstriction is maintained by the endothelium, and the disruption of this balance leads to endothelial dysfunction and causes damage to the arterial wall. Endothelial cells are also responsible for the maintenance of blood fluidity and restoration of vessel wall integrity when injured to avoid bleeding. Endothelial cell-derived factors are also critical mediators of VSMC growth and inflammation. 