ECG determines whether there is myocardial ischemia, mainly observing the changes of ST segment and T wave on ECG. Myocardial ischemia can be divided into acute and chronic, which are pathologically very different and have many similarities and uncertainties in ECG manifestations. The ECG manifestation changes in chronic myocardial ischemia are non-specific and mainly manifest as changes in the negative pole of the ventricle, i.e. ST-T changes. Sometimes it can also affect the ventricular depolarization. T-wave changes can be classified as T-wave hypoplatia, T-wave bidirectionality, T-wave inversion and T-wave hyperacusis. Coronal T, also known as arrowhead T, refers to T-wave inversion in the shape of an isosceles triangle, with two branches of the inverted T-wave symmetrical, with an angle of ≤60° in the middle, like an arrowhead. Coronal T is usually the ECG manifestation of chronic or acute coronary artery supply deficiency. Dynamically changing coronary T is a manifestation of acute myocardial ischemia, while persistent coronary T may be primary chronic myocardial ischemia or secondary myocardial ischemia. Coronary ischemia mainly affects the negative ventricular processes, and the ECG shows ST-T changes. Ischemic T-wave changes are mainly manifested as T-wave hypoplasia, T-wave bidirectional, and T-wave inversion. Among the T-wave changes, coronal T is of great significance for the diagnosis of myocardial ischemia. Myocardial ischemia ECG changes are not unique to coronary artery disease, any heart disease and many pathologies, even healthy people can also present similar ECG.