Heart rate variability is the fluctuation range of circadian rhythm variation of heart rate, which can be abbreviated as HRV. It mainly reflects the activity of the autonomic nervous system, as well as quantitative assessment of the tension of the sympathetic and vagal nerves of the heart and their balance. This index is widely used in clinical practice and is important for the treatment and prognosis of coronary artery disease, especially for the determination of malignant arrhythmias occurring after myocardial infarction, which allows the clinician to take appropriate therapeutic measures at an early stage, and also provides effective evidence for the prognosis of patients with heart failure due to coronary artery disease. Heart rate variability can also be used for the prevention and etiological diagnosis of vasovagal syncope. An increase in heart rate variability indicates an increase in parasympathetic tone, which is a protective factor for human function.