Nitrate drugs form the free radical nitric oxide. This relaxes smooth muscles that surround arteries and veins, causing them to dilate, which in turn decreases preload and to a lesser extent, afterload. Sublingual nitroglycerin is used during angina to rapidly dilate coronary arteries and improve blood flow to heart muscle. The drugs are not “clot busters” (e.g. tPA), they do not stabilize plaques, nor do they change the contractility of the heart (e.g. digoxin).