Arteriovenous shunts are manifestations of hypoxia in which blood from the pulmonary arteries enters the pulmonary veins without oxygenation and flows through the heart to the systemic organs. Arteriovenous shunts can be divided into anatomic shunts and functional shunts. First, anatomical shunt, a part of blood in pulmonary artery flows directly into pulmonary vein through bronchial vein or arteriovenous traffic branch, this part of blood is still venous blood without oxygenation and contains less oxygen, but this is a normal anatomical condition. Because this part of blood is less, it also does not cause hypoxic manifestation. Second, functional shunt, refers to lung lesions such as pneumonia, emphysema, pulmonary fibrosis, slow obstructed lung, etc., where the ventilation/blood flow ratio is imbalanced. The blood flowing through the lungs cannot be fully oxygenated, so it flows out of the lungs and is pumped into the whole body through the heart.