Nitroglycerin causes vasodilation by relaxing vascular smooth muscle and releasing nitric oxide, dilating veins mainly, and the intensity of dilatation is related to the dose. It is mainly used for the treatment of coronary heart disease and angina pectoris. It takes 1-2 minutes to take effect sublingually, and can be repeated after 3-5 minutes, and can be taken 3 times intermittently sublingually. If the pain is not relieved for more than 20 minutes, immediate medical attention is required. Since nitroglycerin has tolerance when applied continuously for more than 2 weeks, the effect of dilating coronary vessels will be weakened, so the drug is only used for emergency use in coronary heart disease and angina pectoris, and not as a long-term application. The main adverse effect is headache, which can disappear after stopping the drug. Some patients may experience vertigo and postural hypotension, and some patients may experience facial flushing and syncope. It is contraindicated in patients with hypertrophic obstructive cardiomyopathy or hypotension, and not for use in patients with glaucoma.