T-wave alternans (TWA), an ECG phenomenon characterized by beat-to-beat alternation of the morphology, amplitude, and/or polarity of the T wave, are the underlying dispersion of ventricular repolarization. Early reports suggested that under long-QT conditions rapid pacing rates result of alternation of the M-cell APD, leading to exaggeration of transmural dispersion of repolarization during alternate beats, and thus the potential for development of torsade de pointes (TdP)[1]. We report a Chinese 7-year-old boy with long QT syndrome type 3 showed a T wave alternans before and following the ventricular tachycardia and its dynamic change during one year and half follow up. He presented with multiple syncopes from the age of 7 years and was found to share a SCN5A A1180V mutation with two other members of his family[2]. He presented with multiple episodes of syncope and a seizure occurring during exercise 2 days before his admission to a local hospital. Three further episodes of syncope occurred within hours of admission; all were short-lived and followed by complete recovery. Continuous ECG monitoring after presentation showed prolonged QTc and biphasic T waves, multiple episodes of ventricular tachycardia (Fig. 1A). T waves were biphasic with delayed onset predominantly in leads III, aVR aVL, aVF, and V1. Before TdP and follow-up ECGs within 48 h of admission also showed multiple ventricular ectopic beatswith a QTc of 610-720 ms with T-wave alternans (Fig. 1B). Treatment involved administration of a b-adrenergic blocker (propranolol 2 mg/kg). ECGs were recorded monthly after discharge; The boy has been followed-up for a year and a half. No further episodes of VT have been detected. Multiple ECGs obtained later repeatedly showed a prolonged QTc of approximately 470 ms in sinus rhythm without T-wave alternans(Fig. 1C). The other two mutation carriers showed ECG features of LQT3 without clinical symptoms. Transthoracic echocardiography showed normal cardiac structure in all three mutation carriers. The present case suggests that T wave alternans are predict ECG pattern for VT/TdP in LQT3 patents and could disappear during silent period.