Patients with myocardial ischemia will suffer from lack of oxygen due to inadequate blood supply to the heart, and the lips will appear black after lack of oxygen, but myocardial ischemia is not the only disease that causes black lips. In addition, chronic pulmonary insufficiency diseases, such as chronic bronchitis, chronic bronchial dilatation, chronic obstructive pulmonary emphysema, chronic pulmonary heart disease, pulmonary hypertension, etc., can also lead to black lips. Patients with chronic heart insufficiency and heart failure will also have black lips. In addition, patients with poisoning, patients with nitrite poisoning in food poisoning will also show clinical symptoms of black lips. So patients with myocardial ischemia will have the above symptoms, but this symptom is not solely due to myocardial ischemia.