Electrocardiographic repolarization abnormalities can be detected by Principal Components Analysis of the T-wave. In this work we studied the effect of signal averaging on the mean value and reproducibility of the ratio of the 2nd to the 1st eigenvalue (P_CA ²¹) and the absolute and relative T-Wave residuum (T_WR ^rel and T_WR ^abs) in the ECG during ischemia induced by Percutaneous Transluminal Coronary Angioplasty. Results showed that T_WR ^rel and T_WR ^rel evaluated from the average of 10 complexes had lower values and higher reproducibility than those obtained from 1 complex. On the other hand P_CA ²¹ calculated from 10 complexes did not show statistical differences versus the P_CA ²¹ calculated on single beats. The results of this study corroborate that, with a signal averaging technique, the 2nd and the 1st eigenvalue are not affected by noise while the 4th to 8th eigenvalues are so much affected by this, suggesting the signal averaged before calculation of absolute and relative T-wave residuum.