A Holter monitor is a type of ambulatory electrocardiogram (EKG or ECG). Ambulatory means that you are able to walk. This device can record the electrical activity of your heart while you move around to do your usual activities. You might wear it for 24 to 72 hours. The monitor is a lightweight, battery-operated tape recorder. You can wear it on a strap over your shoulder. Or you can wear it around your waist. The monitor is connected by wires to small metal discs (electrodes) taped to your chest.