Background and Objectives : The prevention of sudden death in patients with myocardial infarction (MI) remains therapeutic target. T-wave alternans has been known as heart rate dependent measure of repolarization that correlates with ventricular arrhythmia vulnerability. The goal of this study was to clarify whether microvolt-level T-wave alternans (mTWA) can predict lethal arrhythmic events after MI Methods : The mTWA was analyzed using power-spectral method during bicycle exercise testing in 78 MI patients. Additionally left ventricular ejection fraction (EF), late potential (LP) by signal average electrocardiogrm, standard deviation of consecutive RR intervals (SDNN) as a index of heart rate variability were measured. Results : The mTWA was positive in 16 patients (21%), negative in 36 (46%) patients and indeterminate in 21 (33%) patients. Lethal arrhythmic events were developed in 7 patients (3 sudden death, 3 ventricular tachycardia, 1 ventricular fibrillation) during a mean follow-up of 12짹3 months. The events rate was significantly higher in patients with mTWA [relative hazard (RH) 12.0, 95% confidence interval (CI) 1.2 to 118.1, P= 0.01] or lower EF (RH 11.0, 95% CI 1.9 to 65.0, P=0.002). The negative predictive value of mTWA was higher (97%) than its sensitivity, specificity and positive predictive value (80%, 75% and 25%, respectively). Conclusions : mTWA was closely related to lethal arrhythmic events in patients with MI. mTWA is a useful screening test for the prediction of lethal arrhythmic events after MI.