The holter monitor

The holter monitoring is one of the tests cardiologists order to monitor the patient’s heart in relation to chest pain onset. This allows for the doctor to monitor through the printed report the heart’s rhythm and find out any irregularity.
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. While you wear the monitor, it records your heart's electrical activity. You should keep a diary of what activities you do while wearing the monitor. After 24 - 48 hours, you return the monitor to your doctor's office. The doctor will look at the records and see if there have been any irregular heart rhythms.
It is very important that you accurately record your symptoms and activities so that the doctor can match them with your Holter monitor findings. (soruce medline plus)
It is like an EKG worn 24 hours.