Thoracic leads are, as the name implies, the leads distributed in the chest. The thoracic leads are an important part of the normal 12-lead ECG and are located as follows: on the left and right side of the sternum, in the flat fourth rib space, are thoracic lead 2 and thoracic lead 1, respectively (in men, leads 1 and 2 are usually in the flat nipple line). The thoracic 1 and 2 leads generally correspond to the anterior lateral wall of the heart; the thoracic 3 lead needs to be positioned after the thoracic 4 lead is defined; the thoracic 4 lead is located at the intersection of the left midclavicular line and the fifth rib space in the left thoracic position. The thoracic 2 leads are connected to the thoracic 4 leads, and the midpoint of this connection is the thoracic 3 leads. The thoracic 5 and thoracic 6 leads are located on the left posterior side of the thoracic 4 lead. The intersection with the anterior axillary line above the level of the fifth rib space at the left edge of the sternum is the thoracic 5 lead, and the intersection with the mid-axillary line is the thoracic 6 lead. For special patients, it is also necessary to perform the localization of thoracic leads 7, 8, and 9, which are also at the level of the fifth rib space of the left thorax and the intersection of the fifth rib space with the posterior axillary line, scapular line, and paraspinal line, respectively.