How does nitroglycerin relieve the symptoms of angina pectoris?

Nitroglycerin is an organic nitrate that is metabolized to nitric oxide (NO) in vascular smooth muscle. NO activates guanylate cyclase, increasing cGMP, which causes smooth muscle relaxation and vasodilation. Its primary antianginal effect is through venodilation, which reduces venous return (preload) and thus decreases myocardial oxygen demand. Nitroglycerin also causes coronary artery vasodilation, improving blood flow to ischemic myocardium, and mild arterial vasodilation, reducing afterload. The net result is relief of anginal pain by reducing myocardial oxygen demand while improving supply. In the dental setting, sublingual nitroglycerin (0.4 mg) is the emergency treatment for stable angina that does not resolve with cessation of treatment.