Heart block


Heart block is a problem in the electrical signals in the heart.

Normally, the heart beat starts in an area in the top chambers of the heart (atria). This area is the heart's pacemaker. The electrical signals travel to the lower chambers of the heart (ventricles). This keeps the heart beat steady and regular. 

Heart block occurs when the electrical signal is slowed down or does not reach the bottom chambers of the heart. Your heart may beat slowly, or it may skip beats. Heart block may resolve on its own, or it may be permanent and require treatment.

There are three degrees of heart block. First-degree heart block is the mildest type and third-degree is the most severe.

First-degree heart block:

  • Rarely has symptoms

Second-degree heart block:

  • The electrical impulse may not reach the lower chambers of the heart.
  • The heart may miss a beat or beats and may be slow and irregular.
  • You may feel dizzy, faint, or have other symptoms.

Third-degree heart block:

  • The electrical signal does not move to the lower chambers of the heart. In this case, the lower chambers beat at a much slower rhythm, and the upper and lower chambers do not beat at the same rate.
  • The heart fails to pump enough blood to the body. This can lead to fainting and shortness of breath.
  • This is an emergency that needs medical help right away.

Alternative Names

AV Block; Arrhythmia; First-degree heart block; Second-degree heart block; Mobitz type 1; Wenckebach's block; Mobitz type II; Third-degree heart block; Pacemaker - heart block


Heart block may be caused by:

  • Medicine side effects. Heart block can be a side effect of digitalis, beta-blockers, calcium channel blockers, and other medicines.
  • A heart attack that damages the electrical system in the heart.
  • Heart diseases, such as heart valve disease and cardiac sarcoidosis.
  • Some infections, such as Lyme disease.
  • Heart surgery.

You may have heart block because you were born with it. You are more at risk for this if:

  • You have a heart defect.
  • Your mother has an autoimmune disease, such as lupus.


Talk to your health care provider about your symptoms. The symptoms are different for first, second, and third-degree heart block.

You may not have any symptoms for first-degree heart block. You may not know you have heart block until it shows up on a test called an electrocardiogram (ECG).

If you have second-degree or third-degree heart block, symptoms may include:

  • Chest pain
  • Dizziness
  • Feeling faint
  • Tiredness
  • Heart palpitations -- Palpitations are when your heart feels like it is pounding, beating irregularly, or racing.

Exams and Tests

Your provider will most likely send you to a heart doctor (cardiologist) to check for heart block.

The cardiologist will talk to you about your medical history and the medicines you are taking. The cardiologist will also:

  • Do a complete physical exam. The provider will check you for signs of heart failure, such as swollen ankles and feet.
  • Do an ECG test to check the electrical signals in your heart.
  • You may need to wear a heart monitor for 24 to 48 hours or longer to check the electrical signals in your heart.


The treatment for heart block depends on the type of heart block you have and the cause.

If you do not have serious symptoms and have a milder type of heart block, you will most likely need to:

  • Have regular checkups with your provider.
  • Check your pulse every day.
  • Be aware of your symptoms and know when to call your provider if symptoms change.

If you have second- or third-degree heart block, you may need a pacemaker to help your heart beat regularly.

  • A pacemaker is smaller than a deck of cards and may be as small as a wristwatch. It is put inside the skin on your chest. It gives off electrical signals to make your heart beat at a regular rate and rhythm.
  • Sometimes, if the heart block is expected to resolve in a day or so, a temporary pacemaker will be used. This type of device is not implanted in the body. Instead a wire may be inserted through a vein and directed to the heart and connected to the pacemaker. A temporary pacemaker may also be used in an emergency before a permanent pacemaker can be implanted.
  • Heart block caused by a heart attack or heart surgery may go away as you recover.
  • If medicine is causing heart block, changing medicines can fix the problem. DO NOT stop taking any medicine unless your provider tells you to do so.

Outlook (Prognosis)

With regular monitoring and treatment, you should be able to keep up most of all of your usual activities.

Possible Complications

Heart block may increase the risk for:

  • Other kinds of heart rhythm problems (arrhythmias), such as atrial fibrillation. Talk to your provider about symptoms of other arrhythmias.
  • Heart attack.

If you have a pacemaker, you cannot be near magnetic fields. You need to let people know that you have a pacemaker.

  • DO NOT go through the usual security station at an airport, courthouse, or other place that requires people to walk through a security screening. Tell the security personnel you have a pacemaker and ask for an alternate type of security screening.
  • DO NOT get an MRI without telling the MRI technician about your pacemaker.

When to Contact a Medical Professional

Call your provider if you feel:

  • Dizzy
  • Weak
  • Faint
  • Racing heart beat
  • Skipped heart beat
  • Chest pain

Call your provider if you have signs of heart failure:

  • Weakness
  • Swollen legs, ankles, or feet
  • Feel short of breath


Epstein AE, DiMarco JP, Ellenbogen KA, et al. 2012 ACCF/AHA/HRS focused update incorporated into the ACCF/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities: report of the American College of Cardiology Foundation/American Heart Association Task Force on practice guidelines and the Heart Rhythm Society. J AmColl Cardiol. 2013;61(3):e6-e75. PMID: 23265327 www.ncbi.nlm.nih.gov/pubmed/23265327.

Olgin JE, Zipes DP. Specific arrhythmias: diagnosis and treatment. In: Mann DL, Zipes DP, Libby P, Bonow RO, Braunwald E, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 10th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 37.

Review Date: 
Reviewed By: 
Michael A. Chen, MD, PhD, Associate Professor of Medicine, Division of Cardiology, Harborview Medical Center, University of Washington Medical School, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.