A Holter monitor is a small wearable device that measures and records your heart’s activity (ECG) continuously for 24 to 48 hours or longer depending on the type of monitoring used. The Holter monitor and other devices that record your ECG as you go about your daily activities are called ambulatory electrocardiograms. While regular electrocardiograms (ECGs or EKGs) let your doctor look at your heart’s activity at one point in time during your ECG test, abnormal heart rhythms and cardiac symptoms may come and go. That’s why your doctor may want to evaluate your heart over time while you go about your normal activities. You may be asked to wear a Holter monitor if you have fast, slow or irregular heartbeats called arrhythmias; or if you have experienced shortness of breath, palpitations, dizziness, etc. A holter monitor has no risks and wearing it isn’t painful.