HRV is an electrocardiogram result, which is the heart rate variability, heart rate variability refers to the variation of heartbeat cycle difference, neurohumoral factors and determine the condition and prognosis of cardiovascular diseases, also affected by exercise status, emotional changes, heart rate variability analysis methods are time domain analysis, frequency domain analysis and non-linear analysis. Heart rate variability is influenced by gender, age and environmental factors, and is often used to determine the prognosis of myocardial infarction, the prediction of sudden cardiac death and the severity of heart failure patients. Many cardiovascular diseases such as coronary artery disease, myocardial infarction, heart failure, arrhythmia and hypertension can cause a decrease in HRV. HRV is valuable for assessing cardiac diseases, and the lower the HRV, the more serious the disease is, but one cannot look at one result alone and needs to combine it with clinical symptoms.