The diagnosis of sinus arrhythmia mainly relies on ECG, and the ECG performance of different types of sinus arrhythmia has its own characteristics, as follows: 1. Respiratory sinus arrhythmia: it is manifested as sinus P wave with constant morphology, which can be slightly changed by the change of heart position caused by respiration, and the difference between the longest P-P interval and the shortest P-P interval on the same lead is more than 0.16s, and the P-R interval is about 0.12-0.20s. The difference between the longest P-P interval and the shortest P-P interval on the same lead is greater than 0.16s, and the P-R interval is about 0.12-0.20s. The heart rate changes with respiration, the heart rate increases during inspiration and slows down during expiration, and the heart rate changes in a cycle of about one respiratory cycle; 2, non-respiratory sinus arrhythmia: it is more similar to respiratory sinus arrhythmia, and the difference between adjacent sinus P-P intervals on the same lead is greater than 0.16s, the difference is that the P-P interval changes without relation to the respiratory cycle, and the heart rate often suddenly 3. Ventricular sinus arrhythmia: P-P interval without QRS wave group is more than 0.2s longer than P-P interval with QRS wave group, which is relatively common; P-P interval with QRS wave group is more than 0.2s longer than P-P interval without QRS wave group, which is a variant of ventricular sinus arrhythmia.