Understanding Third-Degree Heart Block

Heart block is a condition in which the electrical wiring system of the heart doesn't work correctly. It usually results in a slow heartbeat that's either regular or irregular. This condition may not cause symptoms.    

With third-degree heart block, the upper chambers of the heart are beating normally, but 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 doesn't work well, because the normal rate in the ventricles is much slower. People with third-degree heart block usually have a very slow heartbeat. Because their heart is beating so slowly, it doesn't 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.

Cross section of heart showing electrical signal blocked at SA node.

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

  • Stopping medicines, if they are causing the heart block

  • Getting a pacemaker

What are possible complications of third-degree heart block?

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

When should I call my healthcare provider?

Call your healthcare provider right away if any of the following occur:

  • Unusual tiredness

  • Weakness or dizziness

  • Unusual drowsiness or confusion

  • Pain that gets worse

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

  • New symptoms

Call 911

Call 911 if you have any of the following:

  • Shortness of breath
  • Chest pain
  • Fainting