Third Degree Heart Block: Symptoms, Causes, Treatment

Medically Reviewed by
Dr. Aman Priya Khanna
Third Degree Heart Block

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Third Degree Heart Block
Medically Reviewed by Dr. Aman Priya Khanna Written by Sparshi Srivastava

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Third degree heart block refers to the complete loss of communication between the atria (upper chambers of the heart) and the ventricles (lower chambers of the heart). In this condition, the signalling mechanism controlling the heartbeat is completely blocked.

The third degree heart block ECG or electrocardiogram results show complete atrioventricular (AV) dissociation (no electrical impulses are visible). Primary symptoms include dizziness and shortness of breath. Let's learn more about its symptoms, causes, diagnosis, treatment, and prevention in this blog.

Disease Name

Third degree heart block

Alternative Name

Third degree AtrioventricularAV Block and Complete heart block


  1. Dizziness
  2. Fatigue
  3. Shortness of breath


  1. Heart attack
  2. Long-term heart diseases
  3. Damage during open-heart surgery


  1. ECG
  2. Implantable loop recorder
  3. Electrophysiology study

Treated by

Cardiologist or Electrophysiologist

Treatment Options

Placement of a pacemaker

What is a Third Degree Heart Block?

The heartbeat is regulated by electrical signals generated from its walls (at the Sinoatrial or SA node). This node guides the cardiac muscles about contraction. The signals travel from the atria (upper heart chamber) to the ventricles (lower heart chamber). When there is a slowdown in the conduction of the cardiac electrical signals, it is called a heart block.

In a 3rd degree heart block, there is a complete conduction failure. No electrical signals reach the ventricles. As a result, the pulse is slow or absent. This condition is uncommon, as less than 0.02% to 0.04% of people suffer.

Stages of Heart Block

Depending upon the extent to which the heart's electrical conductivity is affected, there are three stages of heart blocks:

First-Degree Heart Block

Slowed down electrical activity between the atria and the ventricles.

Second-Degree Heart Block

The electrical signals between the atria and ventricles fail to conduct intermittently. 

Third-Degree Heart Block

It can be of two types:

  1. Congenital - People are born with it, but the symptoms appear later. 
  2. Acquired - Underlying medical conditions or exposure to toxins lead to its development.

Third Degree Heart Block Symptoms

An individual with a third degree AV block is more likely to experience one or more of the following symptoms:

  1. Unusually pale skin
  2. Lethargy
  3. Dizziness
  4. Fainting
  5. Unwillingness to participate in physical activity

While the above are the symptoms of congenital third degree heart block, the symptoms of the acquired form of the condition include:

  1. Fainting or dizziness
  2. Chronic fatigue
  3. Confusion
  4. Pain in the chest (angina)
  5. Shortness of breath

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Causes of Third Degree Heart Block

The causes depend upon whether the blockage is congenital or acquired.

Causes of Congenital Heart Block

The primary cause of the condition is through genetic inheritance. Thus, it is observed in children born to mothers suffering from autoimmune conditions like lupus erythematosus (an inflammatory autoimmune condition in which the immune cells attack healthy tissues).

Antibodies generated by the woman's body in reaction against the autoimmune disease during pregnancy can penetrate the placenta, affect the foetus's heart, and give rise to genetic heart block.

Congenital heart block is also associated with impaired foetal development. Consumption of toxic substances like alcohol and tobacco interferes with the baby's growth in the womb. Thus leading to impaired heart structure and enhanced chances of heart block in infants.

Causes of Acquired Heart Block

Acquired third degree heart block occurs when heart muscle damage occurs. This can happen for several reasons:

  1. Coronary artery disease (plaque build-up in the blood vessels obstructs its flow)
  2. Complication of radiotherapy
  3. Uncontrolled or poorly controlled blood pressure
  4. Severe conditions like diphtheria or rheumatic fever (caused by untreated throat infections)
  5. Cancer that has reached the heart
  6. Trauma to the chest (such as a gunshot or a stab wound)

Some third degree AV blocks are also a result of using certain medications(6), such as:

  1. Beta-blockers
  2. Calcium channel blockers

The classes mentioned above of medicines are used to treat high blood pressure. They work by interfering with the electric signals of the heart, subsequently impairing the cardiac output and causing heart block.

Third-Degree Heart Block Risk Factors

The congenital third degree heart block has its origin in pregnancy. However, the acquired form is associated with several other risk factors.

Some factors that increase an individual's risk for heart blockage include both preventable and non-preventable aspects:

Non-Modifiable Risk Factors

  1. Increasing age leads to the tightening of the cardiovascular system. Prolonged damage gradually causes complete cardiac output failure (third degree heart block).
  2. Neuromuscular diseases such as Duchenne muscular dystrophy are associated with heart block. As the disease progresses, heart tissue enlarges and weakens, often leading to left ventricle dysfunction, which pumps oxygen-rich blood.

Modifiable Risk Factors

  1. Coronary artery disease, associated with plaque accumulation, is a common cause of heart block. Worsened arterial blockages in CAD significantly lower the blood supply. Subsequently leading to a third degree AV block.
  2. Cardiomyopathy forces the heart to pump harder due to significantly reduced artery strength. Thus leading to impaired cardiac function and increased risk of acquiring other abnormalities.
  3. Sarcoidosis can result in the accumulation of inflammatory cells around the heart. It is associated with enhanced damage to the cardiovascular conduction system.
  4. High blood potassium levels (above 5.0-5.5 mEq/L for adults) might inhibit conductivity significantly at the atrioventricular (AV) node in the Purkinje fibres (responsible for appropriate cardiac contraction) and ventricles. 
  5. Hyper and hypothyroidism can also be responsible for third degree heart block. Excessive hormone production can cause heart block, hypertension, and cardiac failure. However, lower hormone activity leads to high cholesterol levels and ventricular irregularities.
  6. Lyme disease (a tick-borne illness in humans) is associated with bacterial interference within the heart. This can cause enhanced damage to the electrical conduction, promoting chances of a complete AV block.

Doctors can perform a thorough evaluation and suggest appropriate treatment modalities. Identifying the primary contributing risks is important to address them and avoid worsening the condition and related symptoms.

Prevention of Third Degree Heart Block 

Congenital third degree heart block can be prevented by providing pregnant mothers with appropriate treatment for autoimmune conditions like lupus and sarcoidosis. This may help reduce their babies' risk of developing the same disease.

It is also strictly advised to pregnant women that they must inhibit tobacco and alcohol intake during pregnancy. This facilitates proper functioning in the womb and promotes healthy foetal growth.

Prevention of acquired third stage heart block is aimed at reducing or managing the risk factors. These include:

  1. Regular exercises like walking and jogging increase heart endurance and promote better functioning.
  2. Eating a diet rich in fibre, antioxidants, and other nutrients. These help lower bad cholesterol, control blood sugar, and maintain blood pressure.
  3. Avoiding smoking and consumption of alcohol to avoid weakening of the cardiovascular system.
  4. Reviewing medication risks.

How are Third Degree AV Blocks Diagnosed?

Congenital third degree heart blocks can be diagnosed during pregnancy using routine ultrasound scans and a Colour Doppler. These can be used to measure how quickly the baby's heart is beating and if there is any flaw in the electrical conduction of the heart. Any abnormality, such as a slow heartbeat, may indicate a heart block.

Acquired third-degree AV blocks can be diagnosed by using a combination of:

  1. Blood tests (such as lipid profile, which measures risks of heart attack)
  2. ECG (to measure the overall electrical activity in the heart)
  3. Magnetic Resonance Imaging or MRI (to diagnose structural defects of the heart)
  4. Thallium scan (to measure blood flow to the heart)

Since the 3rd degree heart blocks are serious, diagnostic procedures are started only after treatment has begun.

Here's what a typical diagnosis looks like:

  1. Complete medical history is taken
  2. Lifestyle factors are considered
  3. Investigations: Non-invasive blood tests and imaging scans like ECG are performed
  4. Testing with a Holter or event monitor enables tracking the heart's rhythm for a prolonged time
  5. Placement of a loop recorder under the skin (continuous measurement of the electrical impulses in the heart)
  6. An electrophysiology study is conducted (an invasive procedure where electrodes are implanted inside veins under local anaesthesia)

How to Prepare for the Doctor Consultation? 

Preparing for an appointment with a cardiologist can be very intimidating for those suspected of having third-degree heart blocks. However, it is important to be well-prepared for your appointment. Here's what you can do:

  1. Take all your medical papers and test reports for your appointment
  2. Always make a prior appointment with the doctor to avoid last-minute squeeze-ins. This will give you ample time with the doctor to discuss the case and allow them to perform a physical evaluation
  3. Make a list of questions you wish to ask your doctor. Some of the questions a patient can ask are:

  1. What are the potential causes and risks of the disease?
  2. What is the best treatment choice?
  3. Can it be prevented entirely?
  4. Do lifestyle and diet changes help in managing it?
  5. How much would the treatment cost?
  6. Does insurance provide coverage for the same?

Third Degree Heart Block Treatment

Treatment of a third degree AV block is usually performed with the least invasive option first. Here's what the treatment may involve:

  1. The doctor may first try an intravenous atropine (medication that slows down the heart). However, this has a low chance of working.
  2. The next option is administering dopamine and epinephrine, two neurotransmitters that support the heart. However, these drugs do not regulate the heart rate.
  3. If these medications do not work, the cardiologist will start the patient on transcutaneous pacing (TCP), which involves placing pads on the skin to conduct electrical signals. This helps restore the normal heartbeat temporarily.
  4. If TCP does not work well, the doctor may place a transvenous pacing. This includes placing a temporary pacemaker through a vein.
  5. If the person needs a pacemaker over the long term, a permanent one is placed surgically.

It is important to understand that treatment varies for each individual, depending on their condition and severity.

The severity of the condition implies that the best-suited treatment is obtained at a hospital. However, conventional techniques of homoeopathy and ayurveda can be employed to regulate the symptoms and prevent the progression. However, seeking appropriate expert advice and guidance is important before implementing any of these conventional methods.

Cost of Third Degree Heart Block Treatment 

The cost of a third degree heart block varies for each individual and depends upon several factors. The prominent contributors to price variations include condition complexity, treatment modality, chosen hospital, doctor, and location.

Surgery Name

Surgery Cost

Percutaneous Coronary Intervention

₹25,000 to ₹80,000

Device Implant

₹1,75,000 to ₹4,50,000

Prognosis and Survival Rate 

The success of treatment after a third degree heart block depends upon the cause of the condition, the severity, and the treatment they receive in the hospital. Complications following a pacemaker implantation are rare and occur in less than 4% of patients.

Some cases of third degree heart block may have a less favourable outlook than others. These include people with anterior myocardial infarction (MI). It is always best to discuss the outlook and prognosis of the treatment with the treating doctor.

Risks of Delay in Third Degree Heart Block Treatment

While first-degree and second-degree heart blocks do not cause serious complications, third degree heart block can result in:

  1. Low cardiac output (reduced blood pumping by the heart) due to reduced heart conductivity
  2. Reduced heart rate is observed due to loss of atrioventricular communication
  3. Irregular heartbeat indicates impaired cardiac functioning. It can cause dizziness and breathing difficulties due to reduced oxygen transport
  4. Syncope (temporary loss of consciousness) is related to hemodynamic instability (irregular blood pressure and supply)
  5. Musculoskeletal injuries (fractures, sprains, strains, etc.) due to falls associated with the fainting episode
  6. Sudden cardiac arrest is the most severe complication of a third degree heart block. It can be fatal (life-threatening) and lead to sudden cardiac death

When to Consult a Doctor?

One must always consult with their healthcare provider if they experience one or more of the following symptoms:

  1. Sudden and excessive dizziness
  2. Frequent fainting
  3. Chronic chest pain
  4. Irregular and increased heart rate
  5. Extensive weakness
  6. Shortness of breath
  7. Unexplained swelling in the ankles, feet or legs

Diet for Third-Degree Heart Block

Diet plays a vital role in the health and recovery of people with third-degree heart block.

Here's what one must remember:

  1. Eat a fiber-rich diet, including leafy vegetables, dry fruits, and whole grains (Mediterranean diets are recommended). These ensure the maintenance of appropriate hemodynamic systems. Balanced nutrient intake also promotes overall health improvement
  2. Avoid drinking alcohol as it leads to high blood pressure and a weakened cardiovascular system
  3. Quit smoking because the toxic substances consumed through it can accumulate in the arteries and form clotting
  4. Avoid eating processed and preserved foods. Such food items are high in saturated fats and salts, promoting plaque formation and worsening blood supply irregularities


Third degree heart block is a severe type of heart block marked by total electrical signal blockage from the atria to the ventricles. The heart rate of persons with this illness is usually less than 45 to 50 beats per minute. Timely diagnosis and surgical intervention are the best ways to manage this condition.

If you or someone you know are experiencing symptoms that indicate a heart block or need expert advice or a second opinion on your condition, visit HexaHealth, a one-stop platform for all your healthcare needs. Hexahealth uses a patient-first approach, unbiased guidance, genuine recommendations and proactive care. Want to know more? Contact our expert now!

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FAQs for Third Degree Heart Block

Third degree heart block is caused by the complete stoppage of electrical conduction between the atria and the ventricles.


3rd degree heart block is primarily caused by:

  1. Autoimmune conditions in a pregnant woman (Congenital third-degree block)

  2. Open-heart surgeries

  3. Blood pressure medicines

  4. Chest trauma

  5. Infections like rheumatic fever (swelling of the heart and joints due to an untreated disease)


A few symptoms that may indicate third degree heart block are:

  1. Chest pain

  2. Shortness of breath

  3. Excessive tiredness

  4. Irregular heartbeat

  5. Fainting


Doctors usually diagnose 3rd degree AV block using the following:

  1. Complete physical evaluation

  2. Detailed medical history using blood tests and scans


A third degree heart block ECG shows the atrial rate as faster than the ventricular rate.


A heart block in the third stage can be dangerous and potentially life-threatening. It can cause reduced cardiac output and sudden cardiac arrest. However, it can be managed surgically.


The treatment option for 3rd degree heart block follows the following sequence:

  1. Intravenous atropine

  2. If the above does not work, dopamine and epinephrine are administered

  3. Transcutaneous pacing (TCP) is done if the above two alternatives fail to help the patient.

  4. Transvenous pacing (a type of temporary pacemaker inserted through a vein)

  5. Pacemaker (long-term solution)


While the first line of treating third degree heart block is injecting medications like atropine, dopamine and epinephrine, a pacemaker is the best long-term treatment.


Lifestyle changes can help manage heart blockage. Such changes include:

  1. Eating a heart-healthy diet

  2. Regular exercise

  3. Avoiding alcohol

  4. Quitting smoking

  5. Effective stress management


Although complete recovery is not guaranteed, symptoms of 3rd degree heart block can be controlled and treated using conventional treatment options.


Since a 3 degree heart block is a serious and life-threatening condition, it is best managed by surgical intervention, which involves the placement of a pacemaker.


3rd degree AV block is the third and most severe stage of heart block. If left untreated, it can result in sudden cardiac arrest and even death. However, it can be managed through early detection and proper diagnosis.


Unfortunately, 3rd degree heart block is not reversible. However, implanting a pacemaker is an effective way to restore the electrical conduction between the heart chambers.


Once a pacemaker has been placed, the patient with third degree heart block is monitored regularly by the treating doctor. This helps determine if the heart is functioning normally or if the patient requires additional treatment.


The most effective way to prevent complete heart blockage is to eliminate the risk factors.


People with this condition often experience loss of unconsciousness and extreme tiredness that can disrupt their normal lives.


It is a severe condition that requires immediate medical intervention.


Third degree AV block cannot go away. However, the electrical conduction in the heart chambers can be restored by surgically placing a pacemaker.



All the articles on HexaHealth are supported by verified medically-recognized sources such as; peer-reviewed academic research papers, research institutions, and medical journals. Our medical reviewers also check references of the articles to prioritize accuracy and relevance. Refer to our detailed editorial policy for more information.

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Disclaimer: The information provided here is for educational and learning purposes only. It doesn't cover every medical condition and might not be relevant to your personal situation. This information isn't medical advice, isn't meant for diagnosing any condition, and shouldn't replace talking to a certified medical or healthcare professional.


Dr. Aman Priya Khanna

Dr. Aman Priya Khanna

MBBS, DNB General Surgery, Fellowship in Minimal Access Surgery, FIAGES

12 Years Experience

Dr Aman Priya Khanna is a well-known General Surgeon, Proctologist and Bariatric Surgeon currently associated with HealthFort Clinic, Health First Multispecialty Clinic in Delhi. He has 12 years of experience in General Surgery and worke...View More


Sparshi Srivastava

Sparshi Srivastava

B.Tech Biotechnology (Bansal Institute of Engineering and Technology, Lucknow)

2 Years Experience

An ardent reader, graduated in B.Tech Biotechnology. She was previously associated with medical sciences secondary research and writing. With a keen interest and curiosity-driven approach, she has been able to cont...View More

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