If a patient has a black and purple lip, which is called cyanosis in medicine, the first thing to consider is that the patient has cardiogenic factors, such as unstable angina pectoris in coronary artery disease, or acute myocarditis, pericarditis, infective endocarditis, and myocardial ischemia caused by various factors, there will be a black and purple lip, usually because of coronary artery ischemia, stenosis, spasm, or myocardial cell blood supply This is usually caused by coronary artery ischemia, stenosis, spasm, or insufficient blood supply to the heart muscle cells, and insufficient oxygen supply. In addition, patients with dark and purple lips should also consider respiratory diseases, such as chronic obstructive pulmonary disease, chronic obstructive pulmonary emphysema, chronic pulmonary heart disease, or pulmonary hypertension, which may also have dark and purple lips. If the patient suddenly develops dark purple lips, consider poisoning, such as food poisoning, drug poisoning, and often in the case of nitrite poisoning, this typical symptom is present.