Complete heart block

Complete heart block - sometimes called third-degree AV heart block - is an abnormal heart rhythm (arrhythmia) that happens when the electrical impulses that control your heartbeat are delayed or blocked.

What is complete heart block?

Complete heart block is the most serious type of AV heart block.  It happens when the electrical impulses that tell your heart when to beat don't pass between the top and bottom chambers of your heart as they should.

A back up system will take over and keep your ventricles beating, but they will beat much slower than normal. This can affect the flow of blood to your body and brain.

Find out more about other types of heart block

What are the symptoms of complete heart block?

In some cases complete heart block can lead to episodes of feeling dizzy or collapsing.  It can make you extremely tired, confused or breathless. It may also cause fluid to build up in your body.

In some people, complete heart block is always there, while in others it comes and goes.

What causes complete heart block?

Most people with complete heart block have an underlying heart condition like coronary heart diseasecardiomyopathy or congenital heart disease

It can also be caused by ageing of the electrical pathways in your heart (meaning you're more likely to get it if you're older), electrolyte imbalances, and some medicines.

Heart rhythms booklet

This booklet describes the heart's normal rhythm and various abnormal rhythms as well as explaining how they're diagnosed and treated.

Order or download


What are the tests and treatments for complete heart block?

Your doctor might recommend that you undergo an ECG to help diagnose complete heart block.

  • If you're an adult with complete heart block that causes you to have a very slow heart rate, it's likely your doctor will suggest that you have a pacemaker fitted.
  • If you have complete heart block that was caused by a heart attack, you may only need a temporary pacemaker. If a normal heart rhythm hasn’t returned a few weeks after your heart attack, you might need to have a permanent pacemaker fitted.
  • If you're a young person with congenital heart disease with second-degree or third-degree heart block but you don’t have a slow heart rate or any symptoms, you may still need a pacemaker, but your specialist will discuss this with you. 

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