Arteriovenous (AV) Fistula: Symptoms, Causes, Diagnosis & Treatment — Complete Guide

Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026

Quick Answer

An arteriovenous fistula is an irregular connection in which blood flows directly from an artery into a vein, skipping the capillaries, so tissues below receive less blood [1]. It usually occurs in the legs [1]. Small fistulas may need only monitoring, but large untreated ones can cause heart failure [1]. Treatment includes compression, catheter-based procedures and sometimes surgery [2].

What the research says

• Fistulas can follow catheter procedures, and most can be closed from inside the vessel. In a two-centre series of 12 patients whose lower-limb angioplasty was complicated by an arteriovenous fistula (incidence 0.8%), every angioplasty was ultimately successful, and most fistulas were managed with endovascular methods — coil embolization, balloon tamponade, or stent placement — with an overall technical success rate of 80%. (Ananthakrishnan et al., Eur J Vasc Endovasc Surg, 2006) [3]

• Lung fistulas are treated with catheter embolization. A 2026 review states that endovascular embolization is the standard treatment for pulmonary arteriovenous malformations, which cause right-to-left shunting with risks of low oxygen and paradoxical embolization, and that structured long-term follow-up is needed to catch lesions that persist. (Anwar et al., CVIR Endovasc, 2026) [4]

At a Glance

Item	Summary
What it is	Irregular connection between an artery and a vein [1]
Key mechanism	Blood skips the capillaries — tissues get less blood [1]
Most common location	Legs, but can develop anywhere in the body [1]
Small fistulas	Often no symptoms; monitoring may be all that's needed; some close by themselves [1] [2]
Large-fistula symptoms	Bulging purplish veins, limb swelling, low blood pressure, fatigue, heart failure [1]
Causes	Piercing injuries, congenital, genetic conditions, dialysis surgery (4) [1]
Risk factors	Older age, female sex, cardiac catheterization, certain medicines, high blood pressure, higher BMI (6) [1]
Top complication	Heart failure — the most serious complication of large fistulas [1]
Main tests	Stethoscope exam (humming sound), duplex ultrasound, CT angiogram, MRA [2]
Treatments	Monitoring, ultrasound-guided compression, catheter embolization, surgery [2]

What Is an Arteriovenous (AV) Fistula?

An arteriovenous (AV) fistula is an irregular connection between an artery and a vein. To understand [1] why it matters, it helps to know the normal route: usually, blood flows from the arteries to tiny blood vessels called capillaries, and then on to the veins. The nutrients and oxygen in the blood travel from the capillaries to tissues in the body [1].

With an arteriovenous fistula, blood flows directly from an artery into a vein, avoiding some capillaries. When this happens, the tissues below the avoided capillaries receive less blood [1].

A few facts about where these fistulas show up and why they exist:

• AV fistulas usually occur in the legs but can develop anywhere in the body [1].

• An AV fistula may be surgically created on purpose for use in dialysis in people with severe kidney disease [1] — in that case, it is helpful rather than harmful.

• Symptoms depend on where the fistula forms in the body.

• A large untreated arteriovenous fistula can lead to serious complications.

• Treatment options include monitoring, compression, catheter-based procedures, and sometimes surgery.

What are the symptoms of an arteriovenous (AV) fistula?

Small arteriovenous fistulas in the legs, arms, lungs, kidneys, or brain often won't have any signs or symptoms at all [1]. Small fistulas usually don't need treatment other than monitoring by a healthcare provider [1].

Large arteriovenous fistulas may cause these signs and symptoms:

Symptom	What you notice
Purplish, bulging veins	Veins bulge and show through the skin, similar to varicose veins [1]
Swelling	Swelling in the arms or legs [1]
Decreased blood pressure	Lower-than-normal blood pressure readings [1]
Fatigue	Feeling unusually tired
Heart failure	The heart weakens from the extra workload

When the Fistula Is in the Lungs

A significant arteriovenous fistula in the lungs is called a pulmonary arteriovenous fistula, and it is a serious condition that can cause:

• Pale gray or blue lips or fingernails due to lack of blood flow — this is called cyanosis [1].

• Clubbing — fingertips spread out and become rounder than normal [1].

• Coughing up blood [1].

An arteriovenous fistula in the digestive tract can cause gastrointestinal (GI) bleeding [1].

When to See a Doctor

If you have signs or symptoms of an arteriovenous fistula, make an appointment to see your healthcare provider. Early detection of an arteriovenous fistula may make the condition easier to treat. It may also reduce the risk of developing complications, including blood clots or heart failure [1].

What causes an arteriovenous (AV) fistula?

Arteriovenous fistulas may be present at birth (congenital) or they may occur later in life (acquired) [1]. The four known causes are:

Cause	How it happens
Injuries that pierce the skin	A gunshot or stab wound on a part of the body where a vein and artery are side by side [1].
Congenital fistulas	In some babies, the arteries and veins don't develop properly in the womb. It's unclear exactly why this happens [1].
Genetic conditions	A genetic disease causes irregular blood vessels throughout the body, especially in the lungs. One such disease is Osler-Weber-Rendu disease, also known as hereditary hemorrhagic telangiectasia [1].
Dialysis-related surgery	People with late-stage kidney failure may have surgery to create an AV fistula in the forearm to make dialysis easier to perform [1].

What are the risk factors for an arteriovenous (AV) fistula?

Certain genetic or congenital conditions raise the risk of arteriovenous fistulas, and several other factors may also contribute. Other potential risk factors include:

1. Older age.

2. Female sex.

3. Cardiac catheterization — especially if the procedure involves the blood vessels in the groin [1].

4. Certain medications — including some blood thinners (anticoagulants) and medications used to control bleeding (antifibrinolytics) [1].

5. High blood pressure.

6. Increased body mass index (BMI) [1].

What are the complications of an arteriovenous (AV) fistula?

An untreated arteriovenous fistula can cause complications, and some of them may be serious.

Complication	What happens
Heart failure	The most serious complication of large AV fistulas. Blood flows more quickly through a fistula than through typical blood vessels. The increased flow makes the heart pump harder, and over time the strain on the heart can lead to heart failure [1].
Blood clots	A fistula in the legs can cause clots to form, leading to deep vein thrombosis (DVT). DVT can be life-threatening if the clot travels to the lungs (pulmonary embolism). Depending on where the fistula is, it may also lead to a stroke [1].
Leg pain (claudication)	The fistula can block blood flow to muscles, causing leg pain due to lack of blood flow [1].
Internal bleeding	Fistulas may cause bleeding in the stomach and intestines [1].

How is an arteriovenous (AV) fistula diagnosed?

To diagnose an arteriovenous fistula, a healthcare provider may use a stethoscope to listen to the blood flow in the arms and legs. The blood flowing through an AV fistula makes a sound like humming [2].

If your provider suspects a fistula, other tests are typically done to confirm the diagnosis:

Test	What it does
Duplex ultrasound	The most effective and common way to check for an AV fistula in the legs or arms. Sound waves evaluate the speed of blood flow [2].
CT angiogram	An imaging test that can show whether blood flow is bypassing the capillaries. Contrast dye is given by IV to help the blood vessels show up more clearly [2].
MRA (magnetic resonance angiography)	Done if signs point to a fistula deep under the skin. Like an MRI, an MRA uses a magnetic field and radio waves to create pictures of the body's soft tissues, with contrast dye given by IV [2].

How is an arteriovenous (AV) fistula treated?

The good news about small fistulas: if an arteriovenous fistula is small and doesn't cause any other health problems, close monitoring by a healthcare provider may be the only treatment needed [2]. Some small AV fistulas even close by themselves without any treatment [2].

If treatment is required, your provider may recommend:

Treatment	What happens	Recovery
Ultrasound-guided compression	An option for a leg fistula that's easily seen on ultrasound. An ultrasound probe is pushed down on the fistula for about 10 minutes, destroying blood flow to the damaged blood vessels [2].	Quick, done with ultrasound guidance.
Catheter embolization	A thin, flexible tube (catheter) is inserted in an artery near the fistula. A small coil or stent is placed at the fistula site to reroute blood flow [2].	Many people stay in the hospital less than a day and resume daily activities within a week [2].
Surgery	Large fistulas that can't be treated with catheter embolization may require surgery. The type of surgery depends on the size and location of the fistula [2].	Varies by size and location.

How can people with an arteriovenous (AV) fistula cope and find support?

Finding out you have an abnormal blood vessel connection can be unsettling — especially because some fistulas come with no warning signs at all. Remember that small fistulas often need nothing more than monitoring, and many close on their own. For larger fistulas, modern treatments are minimally invasive: catheter embolization frequently gets people home in under a day, and many are back to normal activities within a week. Keep every follow-up appointment, report any new swelling, bulging veins, or breathing changes promptly, and don't hesitate to ask your provider whether close relatives should be screened if a genetic condition runs in your family.

How should you prepare for an arteriovenous (AV) fistula appointment?

If you think you may have an arteriovenous fistula, make an appointment with your primary care provider. You may be referred to a doctor trained in blood vessel (vascular) or heart (cardiologist) diseases [2].

Appointments can be brief, and there's often a lot of ground to cover — so it's a good idea to be prepared.

What You Can Do

1. Write down any symptoms you're having, including any that may seem unrelated to an arteriovenous fistula.

2. Write down key personal information, including previous piercing injuries or a family history of arteriovenous fistulas or other blood vessel diseases.

3. Make a list of all medications, vitamins, or supplements you're taking, including their doses.

4. Take a family member or friend along if possible. It can be difficult to recall everything said during an appointment, and a companion may remember something you missed.

5. Write down questions to ask your healthcare provider.

Questions to Ask Your Healthcare Professional

1. What's the most likely cause of my symptoms?

2. Are there any other possible causes for my symptoms?

3. What kinds of tests will I need?

4. What treatments are available, and which do you recommend?

5. What's an appropriate level of physical activity?

6. I have other health conditions — how can I best manage these conditions together?

7. Should my children or other biological relatives be screened for this condition?

8. Are there any brochures or other printed material I can take home with me? What websites do you recommend visiting?

What Your Doctor Will Likely Ask

1. When did you first begin having symptoms?

2. Do you always have symptoms, or do they come and go?

3. How severe are the symptoms?

4. Does anything seem to improve the symptoms?

5. What, if anything, makes symptoms worse?

Frequently Asked Questions

What is an arteriovenous fistula?

An arteriovenous (AV) fistula is an irregular connection between an artery and a vein. Normally, blood flows from arteries through tiny capillaries (where oxygen and nutrients reach body tissues) and then into veins. With a fistula, blood flows directly from the artery into the vein, skipping the capillaries — so the tissues below receive less blood.

Are AV fistulas always a problem?

No. Small fistulas in the legs, arms, lungs, kidneys, or brain often have no signs or symptoms and usually need nothing more than monitoring. Some small fistulas close by themselves. In fact, fistulas are sometimes created surgically on purpose in the forearm of people with severe kidney disease to make dialysis easier.

What do AV fistula symptoms look like?

Large fistulas may cause purplish bulging veins similar to varicose veins, swelling in the arms or legs, decreased blood pressure, fatigue, and heart failure. A significant fistula in the lungs can cause blue lips or fingernails, rounded clubbed fingertips, and coughing up blood, while one in the digestive tract can cause gastrointestinal bleeding.

What causes an arteriovenous fistula?

Fistulas can be congenital (present at birth) or acquired later in life. The four known causes are piercing injuries such as gunshot or stab wounds where an artery and vein lie side by side, improper artery-and-vein development in the womb, genetic conditions such as Osler-Weber-Rendu disease, and dialysis-related surgery.

How is an AV fistula diagnosed?

A provider can often start by listening with a stethoscope — blood flowing through a fistula makes a humming sound. Confirmation typically uses duplex ultrasound (the most effective and common test for fistulas in the arms and legs), a CT angiogram with contrast dye, or magnetic resonance angiography (MRA) for fistulas deep under the skin.

Can an AV fistula cause heart failure?

Yes — heart failure is the most serious complication of large AV fistulas. Blood flows faster through a fistula than through normal vessels, so the heart has to pump harder. Over time, that strain can lead to heart failure. Leg fistulas can also cause blood clots, deep vein thrombosis, pulmonary embolism, or stroke.

How is an arteriovenous fistula treated?

Small fistulas may need only monitoring. When treatment is needed, options include ultrasound-guided compression (about 10 minutes of probe pressure on the fistula), catheter embolization (a coil or stent is placed to reroute blood flow — often with hospital stays of less than a day), or surgery for large fistulas that can't be treated with embolization.

Conclusion

An arteriovenous fistula is a wiring error in the circulatory system — an abnormal shortcut that sends blood from an artery directly into a vein, bypassing the capillaries where tissues get their oxygen and nutrients. Most small fistulas are silent and harmless enough to simply monitor, and some close on their own. But a large untreated fistula is a different story: it can quietly strain the heart until failure develops, or seed blood clots that travel where they shouldn't. This guide has covered what an AV fistula is, how its symptoms change with location, the four causes and six risk factors, the four complications, and the three treatment paths — including catheter embolization, which often has people home in less than a day. If you notice bulging varicose-like veins, unexplained limb swelling, or unusual fatigue, the smartest move is to see your healthcare provider early, when treatment is easiest.

This article is for general information only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.

References

1. Mayo Clinic. Arteriovenous fistula — Symptoms & causes. Accessed October 12, 2026. https://www.mayoclinic.org/diseases-conditions/arteriovenous-fistula/symptoms-causes/syc-20369567

2. Mayo Clinic. Arteriovenous fistula — Diagnosis & treatment. Accessed October 12, 2026. https://www.mayoclinic.org/diseases-conditions/arteriovenous-fistula/diagnosis-treatment/drc-20369571

3. Ananthakrishnan G, DeNunzio M, Bungay P, et al. The occurrence of arterio-venous fistula during lower limb subintimal angioplasty: treatment and outcome. Eur J Vasc Endovasc Surg. 2006;32(6):675-9. PMID 16968667. https://doi.org/10.1016/j.ejvs.2006.07.004

4. Anwar U, Ahmed S, Aggarwal K, et al. Evolving strategies in pulmonary arteriovenous malformation embolization. CVIR Endovasc. 2026;9(1). PMID 42132980. https://doi.org/10.1186/s42155-026-00702-x