To investigate the effect of calcium concentration in dialysate on the QT interval (QT) and QT interval dispersion (QTd) during hemodialysis(HD) in patients with end stage renal disease (ESRD), Ca 2+ concentrations of 1 25mmol/L (dCa 2+ 1 25), 1 5mmol/L (dCa 2+ 1 5) and 1 75mmol/L (dCa 2+ 1 75) in dialysate were given to 15 ESRD patients for five times. The QT and QTd were measured before and after the five HD sessions. The results showed: With the dCa 2+ 1 25 HD, serum Ca 2+ and plasma calcium were decreased (1 22?0 08 vs 1 17?0 07 mmol/L and 2 43?0 34 vs 2 28?0 16mmol/L, P 0 05). The changes in the QT correlated inversely with the changes in serum Ca 2+ and plasma calcium ( P