The endothelial layer of cells lining the intimal surface of blood vessels is essential for vascular function. The endothelium releases multiple vasodilator and protective factors, including nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor; an imbalance in these factors predisposes individuals to vascular diseases such as stroke. These factors are differentially regulated by vessel size, sex hormones and disease state, therefore playing differential roles in different tissues following vascular injury. In particular, the endothelium-derived hyperpolarizing factor candidate termed epoxyeicosatrienoic acid, plays a prominent role in microvessel function, especially after ischemia, thereby making this signaling pathway an attractive target for therapy in vascular disease, including stroke.