It is not usually necessary to hold your breath when performing an ECG; holding your breath reduces the oxygen supply to the heart muscle and speeds up the heart rate. However, if the doctor lets the tester hold his breath when measuring the ECG, it may be due to the patient’s breathing affecting the heart rhythm and heart rate, which is mostly seen in patients with severe obesity, chronic lung disease or respiratory sinus arrhythmia, etc.1. Severe obesity: patients with severe obesity, due to the thicker layer of fat, the patch is far away from the heart, and the ECG monitoring may be even more insensitive compared to the usual people. If you breathe at this time, with the rise and fall of the chest, it will lead to some deviation of the indicators of the ECG, affecting the diagnosis, therefore, in this group of people to do ECG monitoring, it is sometimes recommended to hold your breath; 2, chronic lung disease: for some patients with chronic lung disease, on the one hand, the chest rise and fall of the chest is greater than the normal people when breathing, which is likely to affect the diagnosis of the electrocardiogram. On the other hand, it may also be in the test of dyspnea when the patient’s heart function to maintain the body operation; 3, respiratory sinus arrhythmia: chest rise and fall on the electrocardiogram can have a certain impact, so hold your breath to do the electrocardiogram can be observed whether the abnormalities reappear. Especially when the patient has respiratory sinus arrhythmia, the ECG performance has a direct relationship with breathing, and breath holding can effectively determine the patient’s condition and understand the cause of the disease. In addition, when performing ECG, patients should avoid other factors that may affect the results. It is necessary to rest for a period of time and then test in a quiet state, do not be overly nervous; also do not take food, drugs, etc. that affect the heart rhythm and heart rate, such as coffee and tea. Wear loose-fitting clothes to facilitate full exposure of the test site, and do not wear clothes that are prone to static electricity or with metal, so as not to affect the measurement results.