If a patient develops a black purple mouth, the following factors are usually taken into account: 1. To consider the factors of poisoning, such as acute nitrite poisoning, or chronic lead poisoning, food poisoning, drug poisoning, all patients will have a black purple mouth. 2. For cardiogenic diseases, such as chronic heart failure, coronary heart disease, unstable angina, myocarditis, pericarditis, infective endocarditis, hypertrophic obstructive Heart disease, heart valve disease, rheumatic heart disease, can cause patients to have black and purple mouth due to insufficient blood supply and oxygen supply to the coronary arteries. 3, chronic respiratory diseases, such as chronic bronchitis, chronic bronchiectasis, chronic obstructive pulmonary emphysema, pulmonary hypertension, can lead to a decrease in arterial oxygen saturation and low partial pressure of oxygen, which can also have the above clinical symptoms.