A holter monitor is a medical device used by a physician to monitor a patient's cardiovascular system during normal activities. A holter monitor is basically an electrocardiograph that a patient wears throughout the day. Lead wires are placed on the patients chest during the day and the monitor is usually clipped the patient's belt. The holter features an event button that is pressed by the patient when they begin to experience their symptoms. The holter then begins recording an ecg that is saved in the holter monitor and later read by the physician. Holters are commonly used to observe occasional cardiac arrhythmias or epileptic events and what triggered them.