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 48 hours or longer. The monitor is a lightweight device. There are different types of monitors. They are worn in different ways. For example, you might wear it on a strap over your shoulder, hooked on a belt, or placed in a pocket. The monitor is connected by wires to small pads or patches (electrodes) taped to your chest.