A 24-hour Holter monitor is an electrocardiographic record of your heart’s activity. The test is done over a 24-hour period of time as you go about your daily activities. It is safe and painless. A Holter monitor is a small box the size of a Walkman or transistor radio. It has five small cables that are attached to electrode patches and placed on your chest. The monitor is attached to your belt or carried in a pouch with a strap around your neck. It records the activity of your heart and is then downloaded and analyzed by the physician. The Holter monitor may be scheduled for several reasons: To investigate chest pain, to investigate irregular, fast, or slow heart rate, or to investigate dizziness or fainting spells. It may also be done to see if a new heart medication you are taking is working properly.