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Holter monitor (24h)


A Holter monitor is a machine that continuously records the heart's rhythms. The monitor is worn for 24 - 48 hours during normal activity.

Alternative Names

Ambulatory electrocardiography; Electrocardiography - ambulatory

How the Test is Performed

Electrodes (small conducting patches) are stuck onto your chest. These are attached by wires to a small recording monitor. You carry the Holter monitor in a pocket or pouch worn around your neck or waist. The monitor runs on batteries.

While you wear the monitor, it records your heart's electrical activity.

  • Keep a diary of what activities you do while wearing the monitor, and how you feel.
  • After 24 to 48 hours, you will return the monitor to your doctor's office.
  • The doctor will look at the records and see if there have been any abnormal heart rhythms.

It is very important that you accurately record your symptoms and activities so the doctor can match them with your Holter monitor findings.

Electrodes must be firmly attached to the chest so the machine gets an accurate recording of the heart's activity.

While wearing the device, avoid:

  • Electric blankets
  • High-voltage areas
  • Magnets
  • Metal detectors

Continue your normal activities while wearing the monitor. You may be asked to exercise while being monitored if your symptoms have occurred in the past while you were exercising.

How to Prepare for the Test

You do not need to prepare for the test.

Your doctor will start the monitor. You'll be told how to replace the electrodes if they fall off or get loose.

Tell your doctor if you are allergic to any tape or other adhesives. Make sure you shower or bathe before you start the test. You will not be able to do so while you are wearing a Holter monitor.

How the Test will Feel

This is a painless test. However, some people may need to have their chest shaved so the electrodes can stick.

You must keep the monitor close to your body. This may make it hard for you to sleep.

Why the Test is Performed

Holter monitoring is used to determine how the heart responds to normal activity. The monitor may also be used:

  • After a heart attack
  • To diagnose heart rhythm problems
  • When starting a new heart medicine

It may be used to diagnose:

Normal Results

Normal variations in heart rate occur with activities. A normal result is no significant changes in heart rhythms or pattern.

What Abnormal Results Mean

Abnormal results may include various arrhythmias. Changes may mean that the heart is not getting enough oxygen.

The monitor may also detect conduction block, a condition in which the atrial electrical activity is either delayed or does not continue into the ventricles of the heart.


There are no risks associated with the test. However, you should be sure not to let the monitor get wet.


Miller JM, Zipes DP. Diagnosis of cardiac arrhythmias. In: Bonow RO, Mann DL, Zipes DP, Libby P, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 9th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 36.

Olgin JE. Approach to the patient with suspected arrhythmia. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 62.

Review Date:5/13/2014
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, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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