Background/Aims: Sudden K removal is thought to be implicated in ECG alterations observed during hemodialysis (HD). The effects of the K removal rate on ECG-derived parameters have been investigated. Methods: Two different hemodiafiltration (HDF) schedules were used for 10 HD patients: the dialysate K concentration was kept constant in HDF<sub>st</sub>, while in HDF<sub>K</sub> it was decreased during the session in order to maintain a uniform plasma-dialysate K gradient. A 12-lead Holter monitor was used to acquire the ECG in the course of the treatments. Classical ECG parameters and overall indices for quantifying ventricular repolarization abnormalities were evaluated. Results: Several ECG parameters were affected by both HD therapies (ST depression, QRS amplitude and QT dispersion), but only indices of the homogeneity of repolarization (PCA-T, E1-T) were significantly affected by the K removal rate. Conclusion: The present study confirms the large impact of HD therapy on ECG. The analysis of the spatial T wave complexity points out the intrinsic arrhythmogenic implications of the K removal rate.