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Heart Blocks

A heart block happens when the electrical impulses that tell your heart when to beat are delayed or blocked as they travel through your heart. Some heart blocks won’t cause any symptoms, but others are more serious.

What is Heart Block?

Heart block happens when the flow of electricity from the top to bottom of the heart is delayed or blocked at some point along the pathway.

There are three main types of heart block:

  • AV (Atrioventricular) heart block 

  • Bundle branch blocks

  • Tachybrady syndrome

AV (Atrioventricular) Heart Block

An AV heart block happens when the electrical impulses are delayed or blocked as they travel between your atria (the top chambers of your heart) and your ventricles (the bottom chambers of your heart).

There are different ‘degrees’ of AV heart block:

  • First-degree heart block, which usually doesn’t cause symptoms or need treatment.

  • Second-degree heart block. 

  • Third-degree (complete) heart block.

Second- and third-degree heart blocks can cause symptoms which include:

  • Dizziness

  • Feeling lightheaded

  • Blackouts

  • Breathlessness

Some people with heart block can have a very low heart rate. In some people, these heart blocks are always there, whilst in other people, they can come and go. AV heart blocks might turn into higher degree AV heart blocks if they're left untreated. 

Bundle Branch Blocks

A bundle branch block is when electrical impulses travel through the ventricles (the bottom chambers of your heart) slower than is normal, because of a block in the electrical pathway. This delay doesn’t cause symptoms. 

The delay or block can happen on the pathway that sends electrical signals to either the left or right side of the ventricles. The blockages can be seen as a particular pattern on an ECG.

There are two types of bundle branch blocks:

  • Left bundle branch block - which could be a sign of an underlying heart condition which you may need treatment for.

  • Right bundle branch block - can happen naturally in people with no heart disease, but can also be caused by an underlying heart condition.

A bundle branch block itself doesn’t need any treatment but if there is an underlying heart condition, you may need treatment for that condition. 

Tachybrady Syndrome

Tachybrady syndrome happens when your heart’s sinus node (your heart’s natural pacemaker) doesn’t work properly.

Your sinus node is responsible for telling your heart when to beat. If your sinus node doesn’t work properly, your heartbeat can become too fast or too slow, or switch between fast and slow rhythms.


An example of this is when atrial flutter (a fast heart rhythm) alternates with a slow heart rhythm. There might also be sudden pauses in the electrical activity in your heart, which can make you feel dizzy and lightheaded.

What causes Heart Blocks? 

The cause of heart block will depend on the type you have but can include:

  • Coronary heart disease, including heart attack

  • Congenital heart disease, for example hole in the heart

  • Ageing of electrical pathways in your heart

  • Some lung conditions


However it can also happen naturally in people with a normal heart and no heart problems.

How is Heart Block diagnosed?

Heart block is often diagnosed whilst you're having routine tests for other conditions. An electrocardiogram (ECG) can help to detect heart block, because it measures the electrical activity of your heart. The results of an ECG can also show the type of heart block you have. Your doctor might want you to wear a portable ECG monitor to get a reading of the electrical activity of your heart over a longer period of time.

How is Heart Block treated?

Some heart blocks don’t need any treatment, but some do. The type of treatment you’ll need depends on the cause and symptoms. Your doctor will review the medicines that you are taking, to make sure that they are not causing or contributing to your heart block. Depending on the type of heart block and your symptoms, your doctor may suggest a pacemaker. This sends frequent electrical pulses to keep your heart beating efficiently and is a very effective treatment for heart block.

More information:

For more information about Heart Blocks, you can find guides here by the British Heart Foundation or the NHS.

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