The T wave reflects the process of potential change of rapid repolarization of the ventricle, while the ST segment reflects the process of slow repolarization of the ventricle. In terms of sequence, the ST segment comes first and the T wave comes second. The ST segment is the line segment between the end of the QRS wave cluster and the beginning of the T wave, representing the process of slow ventricular repolarization. The normal ST segment is mostly a line of first-order potentials, sometimes with a slight offset, but in either lead, the ST segment downshift is usually no more than 0.05mV. The T wave represents the change in potential during rapid ventricular repolarization. Normal T-wave morphology is asymmetric in both limbs, with a gentle flat slope in the anterior half and a steeper slope in the posterior half.The direction of the T-wave is mostly in line with the direction of the main QRS wave. There are 12 leads in the limb, and the amplitude of the ST segment and T wave may vary in different leads. If the examination finds that the morphology or amplitude of the ST segment and T wave of ECG has changed greatly, it is recommended to consult the cardiology department in time, improve the detailed examination under the guidance of specialists to exclude the influence of disease, and if the examination finds the disease, take the therapeutic measures at an early date.