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 health care provider's office.
• Your provider 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 provider 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.

You do not need to prepare for the test.

Your provider will start the monitor. You'll be told how to replace the electrodes if they fall off or get loose. Contact your provider if the monitor turns off before the end of the test.

Tell your provider 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.

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.

Occasionally there may be an uncomfortable skin reaction to the sticky electrodes. You should contact your provider's office where it was placed to tell them about it.

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 that may be causing symptoms such as palpitations or syncope (passing out/fainting)
• When starting a new heart medicine

Heart rhythms which may be recorded include:

• Atrial fibrillation or flutter
• Fast heart rate (tachycardia)
• Multifocal atrial tachycardia
• Paroxysmal supraventricular tachycardia
• Slow heart rate (bradycardia)
• Ventricular tachycardia

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

Abnormal results may include various arrhythmias such as those listed above. Some changes may mean that the heart is not getting enough oxygen.

Other than the uncommon skin reaction, there are no risks associated with the test. However, you should be sure not to let the monitor get wet.

Ambulatory electrocardiography; Electrocardiography - ambulatory; Atrial fibrillation - Holter; Flutter - Holter; Tachycardia - Holter; Abnormal heart rhythm - Holter; Arrythmia - Holter; Syncope - Holter; Arrhythmia - Holter

Curtis AB, Tomaselli GF. Approach to the patient with cardiac arrhythmias. In: Libby P, Bonow RO, Mann DL, Tomaselli GF, Bhatt DL, Solomon SD, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 12th ed. Philadelphia, PA: Elsevier; 2022:chap 61.

Olgin JE. Approach to the patient with suspected arrhythmia. In: Goldman L, Cooney KA , eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 49.

Updated 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 C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.