To the Editor,Thank you for this letter regarding our paper entitled “Altered heart rate variability depends on the characteristics of coronary lesions instable angina pectoris.” published in this issue (1).HRV analysis method is still developing constantly, generally including three methods: time domain analysis, frequency domain analysis, and nonlinear analysis. Time and frequency domain analyses are widely applied in clinical practice. The time domain measure is the original and simplest method for deriving HRV but has low sensitivity and specificity (2). Frequency domain measure is also a classic analysis method. The analysis of its result is not of physiological significance and the defect cannot reflect the temporal characteristics of non-stationary signal. In addition, the specificity is not high.According to the report of the Task force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology (3), using frequency domain measure, the analyzed ECG signals must satisfy several technical requirements to obtain reliable information. In several studies, authors have applied time and frequency domain parameters in their studies (4). Meanwhile, many studies have separately used time or frequency domain parameters in their studies (5). In our study (6), according to the related studies, we used time domain parameters, which is the original and simplest method to explore the relationship between HRV and severity of coronary lesions in patients with stable angina pectoris. Furthermore, we provided some information on the duration and parameters of ECG recording used in our analysis of HRV in text of method.In our study (1), conclusion is that HRV may be playing a crucial role in estimating the correlation between the damage of coronary artery and dysfunction of autonomic nerve system. Similar to the vast majority of study results, it multicenter studies with a large sample size and to confirm the clinical application undoubtedly. In table 3, we have shown the correlation between coronary artery disease severity and HRV indicators. In table 4, we have shown the correlation between the number of coronary artery diseasepatients and HRV indicators. In table 5, we have shown the correlation between coronary artery lesion locations and HRV indicators. Sample sizes, Gensini scores, and different aspects differ in each table (4, 5). However, we are yet unclear regarding the views of them expressed in the letter that the group distributions of HRV parameters in tables 3-5 in our study substantially overlap with each other and reduce the clinical applicability of the study results.We sincerely hope that these responses can answer their questions.