There is an abnormal channel between the artery and the vein, which is called an arteriovenous fistula. Since the blood in the artery flows into the accompanying vein through the normal channel, it can cause local vascular lesions in the fistula and hemodynamic changes in the local fistula, peripheral circulation and systemic system. It can exist congenitally or be caused by trauma. Arteriovenous fistula causes part of the arterial blood to flow directly into the vein without passing through the capillaries that should perfuse the tissue. This part of the blood does not undergo material exchange in the tissue and becomes an ineffective circulation, which can cause tissue ischemia and necrosis; total peripheral resistance is reduced, blood pressure drops, and cardiac compensation is increased, and the amount of blood returning to the heart exceeds the heart load, resulting in heart failure. Patients with arteriovenous fistulas show peripheral varicose veins, slightly high local skin temperature, pigmentation, and ulcer formation; there may be vascular murmurs or tremors at the fistula. In the late stage, there is heart enlargement and heart failure.