24-hour ambulatory cardiac monitoring is used to diagnose the presence of arrhythmias and myocardial ischemia. 1. Arrhythmia: In some patients with premature beats, 24-hour ambulatory monitoring can reveal the type and total number of premature beats, which can be used to assess whether the patient needs treatment. Some patients have chronic arrhythmias, such as sick sinus syndrome. 24-hour cardiac monitoring is also needed to evaluate the next step in the treatment program. 2. Myocardial ischemia: Clinically, some patients experience frequent chest pain, which requires 24-hour ambulatory monitoring to see if there is any correlation between the patient’s chest pain and the heart, and if it is angina pectoris, there will be changes in the ST segments on the electrocardiogram. In addition, myocardial ischemia is only meaningful at the onset of symptoms, but it may be too late to do an ECG when symptoms are present, so it is difficult to capture myocardial ischemic changes on the ECG, but the diagnosis can be made definitively with a 24-hour ambulatory electrocardiogram.