Interlead variability of the QT interval in surface 12-lead ECG (i.e. QT dispersion) reflects regional differences in ventricular recovery time and it has been linked to the occurrence of malignant arrhythmias in different cardiac diseases. The purpose of the study was to assess the effect of hemodialysis on QT dispersion in chronic hemodialyzed patients. The data of 34 patients (Male/Female = 21/13, mean age 54 +/- 15 years) on chronic hemodialysis were studied. Simultaneous 12 lead ECGs were recorded pre- and post-hemodialysis in a standard setting. The QT intervals for each lead were measured manually by one observer. Each QT interval was corrected for patient's heart rate: QTc = QT/square route of RR (sec). The maximal QT interval changed from 449 +/- 43 to 469 +/- 41 ms (p < 0.01). The maximal QTc interval increased from 482 +/- 42 to 519 +/- 33 ms (p < 0.01). The QT dispersion changed rom 56 +/- 15 to 85 +/- 12 ms (p < 0.001), and the QTc interval from 62 +/- 18 to 95 +/- 17 ms (p < 0.001). During hemodialysis the serum potassium and phosphate decreased from 5.5 +/- 0.8 to 3.9 +/- 0.5 (p < 0.001), and from 2.3 +/- 0.5 to 1.6 +/- 0.4, respectively, whereas calcium level increased from 2.2 +/- 0.23 to 2.5 +/- 0.22 (p < 0.001). It can be concluded that the hemodialysis increased the inhomogeneity of regional ventricular repolarization. Measurement of QT and QTc dispersion by a cheap and simple bedside method could predict the increased myocardial inhomogeneity in dialyzed patients.