The electrocardiogram is one of the most basic tests for cardiovascular disease. T wave alternans (TWA), which reflects abnormal ventricular repolarization, can easily trigger ventricular tachycardia (VT) and ventricular fibrillation (VF), which are important warning clues for sudden cardiac death (SCD). The late sodium current (INaL) is an important component of the frequency-dependent regulation of cardiac repolarization, and various causes of delayed repolarization can increase INaL. Our study on long QT syndrome (LQTS) found that INaL abnormalities can lead to abnormal myocardial repolarization, producing a giant TWA that triggers VT and VF. VT and VF, and INaL inhibition by the INaL blocker mexilate can terminate this process. This suggests that pharmacological blockade of INaL may be a potential target for the prevention of SCD by ameliorating the different causes of giant TWA and its triggering ventricular arrhythmic events. In this study, we propose to randomize patients with VT/VF triggered by giant TWA to conventional treatment and conventional treatment adds mexiletine treatment to compare the effects of the two treatment regimens on giant TWA and its triggered nonsustained VT, sustained VT, and VF; at the same time, we will compare the effects of mexiletine on giant TWA and its triggered ventricular arrhythmias of various etiologies by intra-group control before and after treatment. The safety and efficacy of the treatment of TWA and its triggered ventricular arrhythmias are compared.