Holter, also known as ambulatory electrocardiography, is the continuous recording of electrocardiograms for 24 hours or longer. Holter is a non-invasive diagnostic tool for cardiovascular disease that provides continuous information about the patient’s ECG activity during the day and night. It is useful for qualitative and quantitative diagnosis of clinical arrhythmias, detection of asymptomatic myocardial ischemia, evaluation of the efficacy of drugs for myocardial ischemia and arrhythmias, selection of indications for pacemaker installation and evaluation of pacemaker function. In clinical practice, the use of ambulatory ECG examination items should be selected according to the patient’s specific situation in order to detect some abnormal ECG changes that are not easily detected by conventional ECG examination.