A Holter monitor is a 24-hour recording of the electrical activity of the heart. The monitor is a diagnostic tool used to record the rate and rhythm of the heart.   

Irregularities such as fast heart rate (tachycardia), slow heart rate (bradycardia) and abnormal rhythms of the heart can be recorded.

Because many irregularities in heart rate or rhythm may not be present all of the time, a standard electrocardiogram (EKG) may miss them.

By recording the heart rate and rhythm continuously for 24 hours throughout the various activity levels a child goes through, there is a greater chance of detecting abnormalities.