Arteriovenous Fistula is a medical condition characterized by an abnormal connection between an artery and a vein. Normally, the artery carries blood to the capillaries, where exchange of oxygen and nutrients between the blood and tissues occur. Blood leaves the capillaries to the vein, which carries blood back to the heart. In arteriovenous fistula, the extra connection between an artery and vein causes the blood to bypass the capillaries, resulting in low blood supply to the capillaries. This condition can be congenital or acquired as a result of some medical procedures or injuries, such as gunshot or stab wound. Small arteriovenous fistula usually exhibits no symptoms and does not require any treatment. However, arteriovenous fistula that develops in the lungs (pulmonary arteriovenous fistula) can be potentially life threatening as it can cause breathing difficulties and infection of heart valves. Large arteriovenous fistula requires treatment to reroute blood flow as it may lead to potentially fatal complications, such as congestive heart failure and pulmonary embolism. Interestingly, arteriovenous fistula can be artificially created via surgery in the forearms of people suffering from severe kidney failure to make dialysis easier.