A Holter monitor is a battery-operated portable device that records the cardiac rhythm during your habitual activities. Electrodes are installed on the patient’s chest and connected to a smartphone size monitor that can be worn on the chest, on your belt or attached to a strap. The monitor is equipped with a memory card and an EVENT button that is used when abnormal symptoms appear. A description of these symptoms can be written on an EVENT log. The analysis of the recorded data and VENT log allows the clinician to confirm any anomaly of the cardiac rhythm and to associate these anomalies with the reported symptoms. The data can also be used to evaluate if an implanted cardiac stimulator is functioning properly or to adjust medication. The device is typically worn for 24 to 48 hours. In very special cases, this period can be extended to 5 days and beyond.