Twelve-lead ECG is the most commonly used clinical electrocardiogram, which can clearly diagnose arrhythmia diseases and also assist in the diagnosis of acute myocardial infarction, pericarditis and whether there is enlargement of atrial and ventricular chambers. When doing a 12-lead ECG, the patient should be in a lying position, quiet state, or at the same time as the onset of the disease. First, the ECG should be turned on, then the four limb leads should be connected, and care must be taken not to connect the limb leads backwards, which will affect the final ECG interpretation, and then the chest leads should be connected. Generally, lead V1 is at the 4th intercostal space on the right edge of the sternum, lead V2 is at the 4th intercostal space on the left edge of the sternum, lead V4 is at the intersection of the left midclavicular line and the 5th intercostal space, lead V3 is at the midpoint of the line connecting leads V2 and V4, lead V5 is at the intersection of the 5th intercostal space on the anterior axillary line, and lead V6 is at the intersection of the 5th intercostal space on the mid-axillary line.