Small arteriovenous fistulas in the legs, arms, lungs, kidneys or brain often won't have any signs or symptoms. Small arteriovenous fistulas usually don't need treatment other than monitoring by a health care provider. Large arteriovenous fistulas may cause signs and symptoms. Arteriovenous fistula signs and symptoms may include: 
Purplish, bulging veins seen through the skin, similar to varicose veins
Swelling in the arms or legs
Decreased blood pressure
Fatigue
Heart failure
 A significant arteriovenous fistula in the lungs (pulmonary arteriovenous fistula) is a serious condition and can cause: 
Pale gray or blue lips or fingernails due to lack of blood flow (cyanosis)
Fingertips to spread out and become rounder than normal (clubbing)
Coughing up blood
 An arteriovenous fistula in the digestive tract can cause gastrointestinal (GI) bleeding.