What are Vasodilators. Vasodilators are medicines that dilate (widen) blood vessels, allowing blood to flow more easily through. Some act directly on the smooth muscle cells lining the blood vessels. Other have a central effect, and regulate blood pressure most likely through the vasomotor center located within the medulla oblongata of the brain. Vasodilators are used to treat hypertension (high blood pressure), angina and heart failure.