Electrical alternation of QRS waves, which refers to electrical alternation of sinus QRS wave amplitude, morphology time and direction, is commonly seen in various organic diseases, but also in normal subjects. The mechanism of QRS alternans is not known, but it has been suggested that it is a type of intraventricular two-to-one conduction block. In summary, the principle of generation is unclear, but the differential diagnosis of QRS waves is a gradual decrease with a gradual increase in the pattern of respiratory amplitude motion. If inspiration expands and inflates the lung tissue, the voltage conducted on the chest wall decreases and the QRS wave amplitude becomes smaller when the resistance increases, while the opposite occurs if exhalation occurs. The alternating voltage is not related to respiration and shows a large and small vibration morphological pattern, which makes the two easy to differentially diagnose.