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

Ambulatory electrocardiography; Electrocardiography - ambulatory

There is no special preparation for the test. Your doctor will start the monitor. You'll be told how to replace the electrodes should they fall off or become 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.

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.

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. 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. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 62.