ACE inhibitors aren't the only way to relax the blood vessels. Vasodilators are a type of drug that tells the smooth muscle tissue in a blood vessel to relax, kick up its heels and take a load off. As these tiny muscle fibers relax throughout the system, the heart finds it a lot easier to pump blood throughout the body, and blood pressure decreases.
One issue with vasodilators is that they can work too well. Taking them can result in a sudden drop in blood pressure, leaving you seeing stars, sitting down and seeking medical assistance.
These drugs aren't usually used by themselves to treat high blood pressure -- they're often prescribed along with other heart drugs, such as beta blockers, diuretics or ACE inhibitors.