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Heart block

Heart block is a condition where the electrical signals that control your heartbeat are slowed down or blocked as they travel through your heart. Heart block is a type of arrhythmia, which means an abnormal heartbeat.

Your heart's job is to deliver the oxygen in your blood to your body, by pumping blood through your blood vessels. When your heart beats too slowly, it can't pump as efficiently. The usual heart rate for adults is between 60 and 100 beats per minute. Your heartbeat is thought to be too slow if it drops below 50 beats per minute. This can lead to symptoms such as fainting and feeling short of breath.
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Different types of heart arrhythmia
Arrhythmia is a disturbance of the normal electrical rhythm of the heart
An image showing the electrical impluses in a normal heart and a heart with heart block


  • What happens What happens in heart block?

    Your heartbeat is controlled by electrical signals (impulses) that travel through your heart to make it contract. These impulses start in a part of the wall of the right upper chamber (right atrium) of your heart, called the sinus node. They then travel from the atria (the heart's upper chambers) to the ventricles (the lower chambers) through an area called the atrioventricular (AV) node. The AV node helps to synchronise the pumping action of your atria and ventricles. 

    If you have heart block, there is a problem with how these electrical signals are transmitted through your heart. When the problem occurs at the AV node, it prevents the signals being conducted from the atria to the ventricles. This is called AV block. There are three different levels of AV block, which are described below.  

    • First-degree – the electrical signals are slowed as they pass through the AV node. This rarely causes any symptoms. 
    • Second-degree – not all electrical signals reach your ventricles. The signals are delayed to the point that one is blocked altogether, or it may be that every other signal is blocked. This type of heart block may cause dizziness and fainting, but you won't necessarily have any other symptoms. 
    • Third-degree (complete heart block) – this is the most serious type of heart block. No electrical signals reach the ventricles from the atria, so the ventricles eventually produce their own electrical signals (called the escape rhythm). You will usually have a very slow heartbeat (bradycardia) and it can cause you to have blackouts. 
    Heart block can also happen in a group of electrical-conducting muscle fibres called the bundle of His. These come out of the AV node, divide and lead into your right and left ventricles. If you have a problem here, it's called bundle branch block. It can affect the left- or right-hand side of your heart. If you have bundle branch block, you probably won’t have any symptoms but it can be a sign of another heart condition.
  • Symptoms Symptoms of heart block

    Whether or not you have any symptoms from heart block depends on the type of heart block you have and how severe it is. If heart block has caused your heart rate to slow down (especially if it's less than 40 beats per minute), you may:

    • feel dizzy
    • faint or nearly faint
    • feel short of breath
    • have chest pain 
     These symptoms may be caused by problems other than heart block, but if you have any of them, see your GP for advice.

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  • Diagnosis Diagnosis of heart block

    Your GP will ask about your symptoms and examine you. He or she may also ask you about your medical history. Your GP may do some tests to find out if you have any underlying disease or condition that is causing your symptoms. 

    Some medicines, such as beta-blockers, can slow down your heart rate. Your GP will ask you if you're taking any medicines to make sure they're not causing your heart block. Your GP may refer you to a cardiologist for further tests. A cardiologist is a doctor who specialises in conditions that affect the heart. 

    You may have an electrocardiogram (ECG). This measures the electrical activity in your heart to see how well it's working. You might need to wear a portable heart monitor over a day or two so your heart can be measured over a period of time. You may also have some blood tests. 

    Depending on the results of these tests, your cardiologist may refer you for the following tests. They will either help confirm the diagnosis of heart block, or they may be done to confirm or rule out another, underlying condition. You will need to have some of these tests in hospital.

    • Chest X-ray. This takes a picture of your heart and other organs.  
    • Tilt table test. This involves you lying down on a table which is then tilted. Your heart rate, rhythm and blood pressure are taken at different points.
    • Electrophysiology studies. In this test, a thin, flexible wire (catheter) is passed through a vein in your groin or your arm to your heart. The wire records your heart's electrical activity.
    • Echocardiogram. This uses ultrasound to produce a clear image of your heart muscles and valves.
    • Cardiac stress testing. This is when you have an ECG while you exercise to see how your heart is working under pressure.
    • Coronary angiography. This is a type of X-ray that uses a dye to show your coronary arteries. It can show if they are narrowed or blocked.
  • Treatment Treatment of heart block

    Your treatment for heart block will depend on how severe it is. If it’s causing significant symptoms or is likely to progress to causing more significant symptoms, then you will need treatment. 

    If you have mild (first degree) heart block, you probably won't need any treatment. If your heart block is caused by taking certain medicines, your doctor can review them. If it’s caused by an underlying condition, that will be the focus of your treatment. 

    If your heart block is more severe, and not caused by medicines or an underlying condition, you will probably need to have a pacemaker fitted. 

    Pacemaker implantation 

    A pacemaker is a small device that monitors your heartbeat and sends electrical signals to stimulate your heart to beat at a specific rate. It only sends signals if your heartbeat slows below a particular level. A pacemaker is implanted under the skin on your chest. It's connected to your heart by one or more leads, which are passed through a vein to your heart. For heart block, pacemakers with two leads (called dual-chamber pacemakers) are normally used. The two leads connect to two different points in your heart – usually your right atrium (upper chamber) and right ventricle (lower chamber). 

    If you need a pacemaker urgently, you may have a temporary pacemaker put in until you're able to have a permanent one fitted. You will probably have your pacemaker fitted under local anaesthesia and sedation. This will completely block pain from your chest area and you will stay awake during the operation. The sedative will help you to feel relaxed. 

    You will usually be able to go home the day after your procedure, once your doctor has checked that the pacemaker is working correctly. 

    Some electrical devices or devices that have strong magnetic fields can interfere with a pacemaker by disrupting its electrical signalling. These include mobile phones and metal detectors, for example, but ask your doctor or clinic for a full list. You will need to make sure you're not in close or prolonged contact with such devices.

  • Causes Causes of heart block

    Causes of heart block include:

    • getting older – your heart may be damaged over time, or substances that affect how electrical signals are transmitted in your heart can build up
    • damage to your heart from having a heart attack
    • coronary artery disease
    • certain medicines, including beta-blockers and calcium channel blockers
    • heart muscle diseases, such as sarcoidosis
    • certain infectious diseases, such as Lyme disease
    • other diseases, such as rheumatoid arthritis and systemic lupus erythematosus
    • conditions you're born with (congenital disorders )
    • surgery on your heart, such as operation on your heart valves
  • Complications Complications of heart block

    Most people who have heart block don't develop complications. However, it's possible for heart block to lead to heart failure or blackouts (fainting). Blackouts can happen if your heart rate becomes so slow that not enough blood reaches your brain. This is known as syncope. Immediately before you blackout, you may look pale and your heart may feel like it's racing. Blackouts can happen for other reasons, so it's important to visit your GP for advice.
  • FAQs FAQs

    Does having a slow heart rate mean I have a heart block?


    No, there are lots of things that can cause a slow heart rate, which is called bradycardia. Many people who are physically active have hearts that beat more slowly than usual – this doesn't mean that there's anything wrong.


    Many athletes or people who are physically very fit have hearts that beat more slowly than usual. This is because the amount of exercise they do over time physically changes the structure and function of their heart. Some athletes have been found to have a heart rate of below 50 beats per minute when they are resting. This is perfectly normal for them. However, for most adults, a heart rate is considered to be unusually slow if it drops below 50 beats per minute at rest. 

     A slow heartbeat can be caused by:

    • a heart attack
    • certain medicines
    • hypothermia (when your body temperature drops too low)
    • an underactive thyroid (hypothyroidism)
    • a rise in the pressure inside your brain
    • infections, such as typhoid 
    Another condition that can slow your heart rate is sinus node disease (or sick sinus syndrome). This happens when your heart's natural pacemaker (the sinus node) doesn't work properly. Sinus node disease is more common in elderly people who often have another type of heart disease too.

    Will I be able to feel the pacemaker?


    You may be aware of the pacemaker at first and it may feel uncomfortable to lie in certain positions. However, most people quickly get used to it. Once your surgical wound has healed, you’re unlikely to find the pacemaker uncomfortable. You probably won't be aware of the pacemaker's effects on your heart.


    A pacemaker is small (smaller than a matchbox) so it can be put under the skin on your chest, usually near your collarbone. You may be able to feel the pacemaker box and connecting leads under your skin as the wound heals. It's very important that you don't try to move them. Let your doctor know if they continue to bother you. 

    Your pacemaker will be programmed while you're in hospital to the best settings for you, so you shouldn't be aware of it working. However, if you felt your heartbeat was slow before it was fitted, then you may notice your heart beating faster.

    Can I exercise or play sports with a pacemaker?


    You will be able to exercise and play most sports when you have fully recovered from the procedure to fit your pacemaker. However, if you want to play contact sports, you may need to take extra care. 


    Your doctor might advise you not to do any strenuous activity until after you have been to your pacemaker follow-up appointment. This will be about six weeks after you have the pacemaker fitted. Strenuous activity includes sports and heavy lifting, for example. 

    After your follow-up appointment, you should be able to increase your level of activity and start to exercise or play sports again. If you want to play contact sports, wear a protective pad over your pacemaker to help protect it if you get a knock. 

    It's important to get back to exercising after you recover from having a pacemaker fitted. It's a good way to keep healthy and reduce your risk of heart disease.

    How long will my pacemaker last?


    A pacemaker battery usually lasts between six and 10 years. You will have regular check-ups to predict when you will need a new one. It won't be allowed to completely run down. 


    You will usually have check-ups every three months to a year depending on the type of pacemaker you have fitted and how well it's working. Some types of pacemaker allow your clinic to monitor its effect remotely. Any problems or changes in your pacemaker’s function can be picked up quickly and the clinic will contact you to come in if necessary. Your clinic will aim to fix any such problems by reprogramming your pacemaker during your check-up. 

    Most of the pacemaker box is taken up with the battery, so the whole box is replaced when the battery shows signs of wear. The leads of the pacemaker are usually left in place but these may need to be replaced eventually. Your healthcare team will assess the leads during your check-ups. Replacing a pacemaker box is a minor procedure (less complex than when your pacemaker was originally fitted), and is usually done under local anaesthesia. 

    For more information, speak to your doctor.

  • Resources Resources

    Further information


    • ECG identification of conduction disorders. PatientPlus., reviewed 25 January 2013 
    • What is heart block? National Heart Lung and Blood Institute., published 9 July 2012 
    • Cardiovascular system anatomy. Medscape., published 20 August 2014 
    • Target heart rates. American Heart Association., published 8 January 2015 
    • Sinus bradycardia. Medscape., published 18 December 2014 
    • Dual-chamber pacemakers for symptomatic bradycardia due to sick sinus syndrome without atrioventricular block (part review of technology appraisal guidance 88). National Institute for Health and Care Excellence (NICE), November 2014. 
    • About arrhythmia. American Heart Association., published 23 October 2014 
    • Atrioventricular block. BMJ Best Practice., published 25 April 2014 
    • Atrioventricular block. Medscape., published 18 December 2014 
    • Understanding the heart's electrical system and EKG results. National Heart Lung and Blood Institute., published 9 July 2012 
    • Bundle branch and fascicular block. The Merck Manuals., published July 2012 
    • Map of Medicine. Bradyarrhythmias. International View. London: Map of Medicine; 2011 (Issue 2) 
    • Bradycardia. BMJ Best Practice., published 24 September 2014 
    • X-ray (radiography) – chest. RadiologyInfo., published 16 May 2014 
    • Tilt-table testing technique. Medscape., published 20 November 2014 
    • Treadmill stress testing. Medscape., published 18 March 2014 
    • Cardiac catheterisation. PatientPlus., reviewed 21 December 2012 
    • Brignole M, Auricchio A, Baron-Esquivias G, et al. 2013 ESC guidelines on cardiac pacing and cardiac resynchronization therapy. Eur Heart J 2013; 34:2281–329. doi:10.1093/eurheartj/eht150  
    • Inserting temporary pacemakers. PatientPlus., reviewed 12 August 2014 
    • Syncope clinical presentation. Medscape., published 16 April 2014 
    • Bradycardia. PatientPlus., reviewed 18 February 2011 
    • Athlete’s heart. The Merck Manuals., published December 2014 
    • Pacemakers. British Heart Foundation., published 1 April 2012 
    • Pacemakers and implantable cardioverter-defibrillators. Medscape., published 2 May 2014 
    • Pacemaker. Arrhythmia Alliance., published 2012 
    • Pacemakers and pacing. PatientPlus., reviewed 19 September 2014 
    • Start active, stay active: a report on physical activity for health from the four home countries’ chief medical officers. Department of Health., published 2011 
    • How will a pacemaker affect my lifestyle? National Heart Lung and Blood Institute., published 28 February 2012
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