Vasodilators are medications that open (dilate) blood vessels. They work directly on the muscles in the walls of your arteries, preventing the muscles from tightening and the walls from narrowing. The blood flows more easily through your arteries, your heart doesn't have to pump as hard and your blood pressure is reduced. The best vasodilators depend on the health and the condition being treated. The use of vasodilators to prevent, treat or improve symptoms in a variety of conditions, such as high blood pressure, high blood pressure during pregnancy or childbirth (preeclampsia or eclampsia), heart failure and high blood pressure that affects the arteries in your lungs (pulmonary hypertension)