Understanding Third-Degree Heart Block

Heart block is a condition in which the electrical wiring system of the heart does not work properly.  It usually results in a slow heartbeat that is either regular or irregular. This condition may or may not cause symptoms in patients.   

With third-degree heart block, although the upper chambers of the heart are beating normally, the electrical signals are not relayed from the upper chambers of the heart (atria) to the lower chambers (ventricles). The signaling system in the lower chambers may take over as a backup, but this does not work well as the intrinsic rate in the ventricles is significantly slower. People with third-degree heart block usually have a very slow heartbeat. Because their heart is beating so slowly, it does not do a good job of sending blood throughout the body. People with heart block often have symptoms.

Third-degree heart block is sometimes called complete heart block.

What causes third-degree heart block?

Third-degree heart block may be caused by:

  • Damage to the heart from surgery

  • Damage to the heart muscle from a heart attack

  • Other types of heart disease that result in heart muscle damage

  • Heart valve disease

  • Other diseases, including rheumatic fever and sarcoidosis

  • Some medicines

  • Older age

In addition, some babies are born with heart block. Heart block may also run in families.

What are the symptoms of third-degree heart block?

Symptoms of third-degree heart block may include:


  • Lightheadedness, faintness, or dizziness

  • Feeling tired

  • Shortness of breath

How is third-degree heart block treated?

Third-degree heart block is a serious condition that needs to be treated right away. Treatments for third-degree heart block include:

  • Taking medicines to increase the heart rate for the short-term (acutely)

  • Stopping medicines, if they are causing the heart block

  • Getting a pacemaker

What are the complications of third-degree heart block?

Third-degree heart block may cause a sudden loss of consciousness. It also may cause the heart to suddenly stop beating (sudden cardiac arrest).

When should I call my healthcare provider?

Call your healthcare provider right away if you have any of these:

  • Unusual tiredness

  • Shortness of breath

  • Chest pain

  • Weakness, dizziness, or fainting

  • Unusual drowsiness or confusion

  • Pain that gets worse

  • Symptoms that don’t get better with treatment, or symptoms that get worse

  • New symptoms

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