When a clinician suspects a problem with a patient’s heart “circuitry,” he or she prescribes an ambulatory electrocardiogram (ECG), in which the patient carries a “box” for 24 hours (or even 48 hours or more), then takes it off and connects it to a computer for data analysis. The patient is given a report detailing the “signals” emitted by the heart while carrying the “box”. An ECG, also known as a Holter, is an important adjunct to modern medicine and can capture certain atypical cases more accurately than a single electrocardiogram. For example, some paroxysmal arrhythmias come and go quickly, and sometimes the patient is not in the hospital and an ECG cannot be performed immediately, but with an ambulatory ECG, it can be captured. Syncope due to certain cardiogenic diseases can also be identified by ECG. It is often used in daily life, but not limited to the following situations: 1) monitoring various heart rhythms, heart rates and conduction; 2) for patients with unexplained dizziness, darkness and syncope; 3) for the diagnosis of sinus syndrome and deciding whether to install a pacemaker; 4) for the follow-up of pacemaker installation and monitoring pacemaker-induced arrhythmias; 5) for the observation of the efficacy of antiarrhythmic therapy. During the wearing of ECG, the following matters should be noted: 1. The skin should be dry and not wet. 2, away from strong electromagnetic fields, but daily telephone use is not restricted. 3, wear during the occurrence of discomfort, to record in detail in order to help doctors targeted analysis of the situation at the moment.