HealthSheets™


Understanding Third-Degree Heart Block

Cross section of heart showing conduction system.

Heart block is a condition in which the electrical wiring system of the heart does not work properly.  Sometimes it can result in a slow heartbeat that is either regular or irregular. This may cause symptoms.   

With third-degree heart block, 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. People with third-degree heart block usually have a very slow heartbeat. Their heart does not do a good job of sending blood throughout the body. They usually 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

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:

  • Chest pain

  • 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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