Objective: Microvolt T-wave Alternans (TWA) is associated with abnormal repolarization and predicts arrhythmic mortality in patients with previous myocardial infarction (MI). Infarct tissue size and heterogeneity characterized by cardiac magnetic resonance (CMR) has been shown to be associated with arrhythmogenic substrates and sudden cardiac death. Although both delayed enhancement-CMR (de-CMR) and TWA are useful in risk stratification of post-MI patients with preserved left ventricular function, the relationship between scar size and TWA has not studied yet. In this study, we aimed to study the relation between TWA and scar size and characteristics assessed with CMR in post-MI patients (pts) with relatively preserved systolic function presented with nonsustained VT. Methods: This observational cross-sectional study was enrolled 36 post-MI patients with mild-systolic dysfunction and non-sustained ventricular tachycardia. Eight pts were excluded. Both TWA and contrast enhanced CMR were performed. Left ventricular ejection fraction (LVEF), dense scar, peri-infarct zone and total scar masses were assessed and these values to left ventricular (LV) mass ratios were calculated. Infarct ratios and characteristics were determined and compared among patients with negative TWA and those with positive TWA. Results: For the positive (n=12) versus negative (n=16) TWA patients there were no significant difference between LVEF (44.9±5.4% vs. 44.0±3.2%, p=NS) and LV masses (121.89±26.56 g vs. 106.14±21.16 g, p=NS). The ratio of scar core to LV mass (3.37±0.68% vs. 3.31±1.01%, p=NS), peri-infarct zone to LV mass (23.61±7.93% vs. 21.64±9.08%, p=NS), total scar to LV mass (26.98±7.86% vs. 24.96±9.62%, p=NS) were all similar. Conclusion: There were no association between scar size and infarct heterogeneity and prevelance of TWA in post-MI patients with relatively preserved LVEF with non-sustained VT. Our data suggest that these two modalities may reflect different arrhythmogenic mechanisms in this cohort.