Arrhythmia is one of the most important causes of mortality in patients on hemodialysis and may develop due to cardiovascular diseases or fluid-electrolyte or acid-base abnormalities. Previous studies have shown that acetate hemodialysis (AHD) increased the frequency of arrhythmia. To evaluate the frequency and the causes of arrhythmias during AHD, we studied 33 randomly selected patients (25 male and 8 female, mean age of 45+/-18 years) who were under AHD (4 h, 3 times/week, mean duration of HD of 38+/-29 months) with the same Cuprophan membranes. All patients underwent a detailed echocardiographic evaluation during the interdialytic period. Twenty-four hours of Holter monitoring was performed starting from the onset of HD. Twelve lead electrocardiography (ECG) was obtained, and venous and arterial blood samples were drawn for serum electrolytes, pH, and arterial blood gas measurements before and after HD. Serum magnesium and potassium levels dropped after AHD (from 2.3+/-0.5 to 1.9+/-0.3 mEq/L and from 5+/-0.7 to 3.4 +/-0.4 mEq/L respectively, p < 0.001); on the other hand serum pH, bicarbonate, sodium, and calcium levels were normalized. Electrocardiographic evaluation revealed significant lengthening of the QTc interval (from 433+/-42 to 464+/-43 ms, p < 0.001), which was thought to be related to the decrease in serum magnesium and potassium levels. The frequencies of ventricular premature contractions (VPCs) were not different during AHD and the interdialytic period (8+/-9.1 to 6.5+/-11 contractions/h, p > 0.05). This was also true for supraventricular premature contractions (SVPCs) and supraventricular tachycardia (SVT). Nonsustained ventricular tachycardia was observed in 2 patients during HD and in 1 patient in the interdialytic period. No relation was established between the echocardiographic findings and the frequency of arrhythmia. In our ambulatory electrocardiographic study, the frequencies of VPCs and SVPCs observed during the interdialytic period were only positively correlated with age (r=0.54, p=0.013 and r=0.50, p=0.010, respectively). No relation was found between the frequency of arrhythmia and the gender of the patients; duration of HD; etiology of kidney disease; or serum Na, K, Ca, iCa, Mg, bicarbonate, or pH levels (p > 0.05). In conclusion, the application of AHD does not increase the frequency of arrhythmia in HD patients as had been shown in previous studies.