The Holter Monitor and Event Monitor are different portable devices that continuously monitor your heart rate and rhythm. They are useful in detecting abnormal heart rhythms that occur intermittently or cause transient symptoms. The Holter Monitor is used to automatically record your heart rate and rhythm over a 24-hour period. This monitor is small enough to be worn beneath clothing. While you wear this monitor, we ask that you keep a diary of what activities you do and how you feel. After 24 hours, you will return the monitor to the ACA office along with the diary you kept. Your cardiologist will look at the recordings to see if there have been any abnormal heart rhythms. The Event Monitor is used when you donít have a rhythm that occurs daily. In this case you manually activate the event monitor when you feel you have an unusual event (rhythm). This monitor needs to be worn over a 30-day period. After 30 days, your cardiologist will analyze the recordings.