Angina is divided into stable angina and unstable angina. Stable angina usually lasts for 3-5 minutes, while unstable angina is more painful and lasts for about 20 minutes and up to 30 minutes. Angina usually occurs in the retrosternal and precordial regions, and patients may feel pressure and burning-like discomfort. Stable angina is most likely to occur after exertion, emotional stress, or satiety, and usually lasts for 3-5 minutes and is usually relieved by sublingual nitroglycerin. Unstable angina attack time is long, but usually not more than half an hour, if the nitroglycerin can not see the effect is not big, and the patient appeared to sweat, vomiting, then should immediately consult a doctor, because it is likely to be an acute heart attack.