People with possible heart problems are sometimes asked to wear a device called a Holter monitor for one or two days. The device measures the electrical activity in the heart. It helps doctors pinpoint heart rhythm problems. You will have “electrodes” stuck to your chest that are connected to wires leading to the monitor. These electrodes tell the monitor how often your heart beats and if it has a normal rhythm. While you have a Holter monitor on, you should do your normal activities but keep the electrodes, wires and device dry. Some people have an abnormal heart rhythm only during certain activities or certain times of the day.