AV block (heart block)

At a glance

  • In AV block (sometimes called heart block), electrical signals don't travel across the heart properly.
  • Mild cases often go unnoticed.
  • But severe AV block makes the heart beat far too slowly, leading to symptoms like dizziness, weakness and fainting.
  • People who have these symptoms usually get a pacemaker.
  • This device makes sure your heart beats fast enough again.


Photo of a couple taking a stroll

A very slow heartbeat can be caused by various things. If it's a heart rhythm disorder, it's often a condition known as AV block (atrioventricular block) or heart block. In this condition, the electrical signals in the heart don’t travel normally from the upper chambers (atria) to the lower chambers (ventricles).

In a healthy person, the heart rhythm is controlled by the sinus node, which is in the right atrium at the top of the heart. The sinus node sends out electrical signals that travel down the atria to the AV node. From there, they move on to the ventricles.

In AV block, these signals don't travel down the heart chambers properly. There are three degrees of severity:

  • First-degree block: The signals are passed on with a delay. The heart still beats rhythmically and at a normal rate.
  • Second-degree block: The signals are sometimes interrupted (blocked). Some signals no longer reach the lower chambers of the heart, and the heart misses a beat once in a while.
  • Third-degree block: The transmission of electrical signals is completely disrupted (complete AV block). No signals reach the lower heart chambers. If this happens, the lower chambers produce their own electrical signals that usually keep the heart beating. The heart then beats very slowly, at less than 40 beats per minute (bradycardia). People with this most severe form of AV block need a pacemaker.


The symptoms will depend on the degree of AV block and whether the heart has also been damaged by another condition.

People who have mild (first-degree) AV block and are otherwise healthy often have no symptoms and don’t even know they have it.

In second-degree and third-degree AV block, symptoms like palpitations, skipped heartbeats, weakness and dizziness are more common. Especially during physical exertion or psychological stress, you may also have difficulty breathing, chest pain or even faint (known as syncope).

In third-degree AV block, the heart beats very slowly. Then these symptoms can even be felt at rest, as soon as the abnormal heartbeat starts. The lower legs may gradually swell too because fluid builds up in the tissue (edema).

Sometimes AV block only occurs over a short time.

Causes and risk factors

There are many possible causes of AV block. Sometimes athletes or teenagers have a mild form at rest – but this form is not considered to be a medical problem.

AV block is a possible side effect of certain medications, including some heart medications, antidepressants or cancer medications. The electrical pathways in the heart can also be disrupted as a result of hormonal disorders, autoimmune diseases and infectious diseases like Lyme disease.

Illustration: In AV block, electrical signals in the heart are disrupted

Severe, permanent AV block is usually the result of a heart condition like a congenital (at birth) heart defect, of the heart muscle (myocarditis) or coronary artery disease (CAD). So risk factors for CAD (like diabetes, high blood pressure, smoking, being very overweight or elderly) also increase the risk of AV block.

Prevalence and outlook

AV block is one of the more common heart conditions. But it’s not possible to say exactly how many people have it. Older people are more likely to develop a severe form, and younger people are more likely to have a mild form.

AV block can occur all the time or only temporarily. For example, mild AV block may temporarily go away as soon as your pulse increases due to strenuous activities. Then it might come back again when you're at rest. Even severe AV block can completely disappear – for example, if you stop taking medicines that are causing it. If AV block is caused by another heart condition, though, it’s often permanent.

In some people, mild AV block turns into severe AV block. This is particularly the case with a special type of second-degree AV block known as “Mobitz type 2." Here the heart regularly skips a beat – for example, every second or third beat. People with Mobitz type 2 have a higher risk of developing complete (third-degree) AV block.


In complete AV block, the heart beats very slowly. As a result, less oxygen-rich blood reaches the tissues and cells of the body. This has many effects: Lack of oxygen in the brain can lead to fainting, which in turn can result in falls and accidents.

The potentially life-threatening consequences of third-degree AV block include cardiac arrest, where the heart stops beating.


Sometimes, AV block is first discovered when a medical professional measures your pulse or listens to your heart. They might notice that beats are “skipped” or the heartbeat is very slow. AV block can be properly diagnosed using an electrocardiogram (ECG): Doctors can recognize AV block and its severity in the ECG graph. Sometimes, special ECG tests are needed, like a stress test or continuous ECG monitoring.

The doctor will ask questions and do a physical examination to try to find out how much the abnormal heartbeat is affecting your life and whether there are signs of any underlying illnesses. This is often followed by other examinations, like blood tests, an ultrasound scan of the heart (echocardiogram), a (MRI) scan, or cardiac catheterization.


The treatment options for AV block mainly depend on whether it's causing symptoms. Mild cases often don't need to be treated. But a is usually needed in more serious cases, like in Mobitz type 2 (second-degree) AV block and in complete (third-degree) AV block. Medicines like atropine or adrenaline (epinephrine) are usually only used in emergencies.

Treatment with a may be temporary – but it is permanent if the cause of AV block can't be treated. The makes sure that the heart beats at a normal rate, but it doesn’t get rid of the root cause of the problem.

If you're deciding whether or not to get a , you can use our decision aid to help you weigh the pros and cons.

Everyday life

People with severe AV block may be distressed by symptoms like difficulty breathing or weakness, as well as worrying about fainting and life-threatening consequences.

But treatment with a affects your daily life too: You have to go for regular check-ups, and you always have to carry your ID card on you. Some people are bothered by the fact that the can be seen under the skin on their chest.

At first, many people with a are worried about breaking it when they move, so they're very careful. These fears are sometimes fueled by friends and family.

Problems in everyday life are generally quite rare, though, and most people get used to their after some time. It helps if the can detect when you’re doing strenuous activities. Like a healthy sinus node, the then sends signals at a faster pace, which allows you to do physically strenuous jobs, sports and hobbies. Driving is usually no problem either. Flying with a is possible too, but it’s important to tell airport security about the . Some people don't feel comfortable doing that.

Pacemakers can be disturbed by nearby electronic and magnetic devices. But problems can be avoided by keeping a safe distance of 30 centimeters to electronic devices. For cell phones, 15 to 20 centimeters are enough. You can keep that distance by simply holding the phone to the ear on the side of the body away from the . For some equipment, like induction stoves, a larger distance may be needed. Some body fat scales can be used by people with pacemakers. It is important to check the instructions to be sure.

The has to be taken into consideration in some medical examinations too. A typical example is (MRI). But there are now many devices that allow you to have an MRI scan, after making certain preparations.

Further information

If you get a , your doctor will usually tell you what to look out for in everyday life. Our list of questions can help you to prepare for your next appointment and figure out what you'd like to ask. If you don’t want to wait until the appointment with your doctor, you can get information from your health insurer.

When people are ill or need medical advice, they usually go to see their family doctor first. You can read about how to find the right doctor in our topic "Health care in Germany."

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Sommer T, Bauer W, Fischbach K et al. MR-Untersuchungen bei Patienten mit Herzschrittmachern und implantierbaren Kardioverter-Defibrillatoren. Konsensuspapier der Deutschen Gesellschaft für Kardiologie (DGK) und der Deutschen Röntgengesellschaft (DRG). Kardiologe 2017; 11: 97-113.

Von Knobelsdorff-Brenkenhoff F, Bauer WR, Deneke T et al. Empfehlungen zu kardialen MRT-Untersuchungen bei Patienten mit Herzschrittmachern und implantierbaren Kardioverter-Defibrillatoren. Kardiologe 2019; 13(2): 75-86.

IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

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Created on November 6, 2023

Next planned update: 2026


Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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