BACKGROUND: Repolarization variability is considered to predict sudden cardiac death (SCD). T-wave alternans (TWA) was subject of exhaustive research, whereas beat-to-beat variability of repolarization (BVR) is a new parameter possibly predicting proarrhythmia. How these parameters interact has not been tested. OBJECTIVE: To compare TWA and BVR as predictors of pro-arrhythmic substrate early after myocardial infarction (MI). METHODS:: In nine pigs, MI was induced by a 1-hour LAD occlusion. Cardiac magnetic resonance imaging (MRI) was performed at day 21. Six sham pigs served as control. Spectral TWA was tested during RA pacing before induction of MI and after 21 days. BVR was calculated from 60 consecutive QT intervals. RESULTS: MRI showed transmural MI. TWA was negative in all pigs at clinical threshold rate and equally present in MI versus sham pigs at higher rates (at 170 bpm: 55 vs. 50% positive TWA). In MI pigs BVR of QT-intervals increased significantly during acute ischemia (2.44 ± 0.43 vs. 3.55 ± 0.41 ms, p<0.01) and even more on day 21 (5.80 ± 1.12 ms), were it differed significantly from shams (2.14 ± 0.54 ms, p<0.01). A clinical VT induction protocol was positive in 2 of 8 MI pigs and in none of 6 shams. CONCLUSIONS: In early remodeling after myocardial infarction, BVR at intrinsic heart rate was a consistent phenomenon, whereas TWA during atrial pacing or baseline QT-interval changes were not. TWA and BVR could reflect different post-MI remodeling processes. BVR may be a new technique to predict a potentially pro-arrhythmic substrate in the early post infarct period.