Two approaches were chosen to assess the controversially debated influence of acetate on the heart in dialysis patients: (1) To separate acetate effects from influences of dialysis, acetate was infused in 12 chronic dialysis patients with normal systolic function on a dialysis-free day, and left ventricular (LV) function was assessed by LV pressure/volume loops. Hyperacetatemia (3-5 mmol/l) resulted in a decrease in LV preload (LV end-diastolic pressure decreased from 16 ± 3 to 10 ± 4 mm Hg, p < 0.01) but had no influence on LV contractility. (2) In 8 dialysis patients without cardiac disease, isovolemic acetate or bicarbonate dialysis was performed. During both procedures, there were comparable changes in serum electrolytes as well as in echocardiographic parameters. LV contractility measured by velocity of circumferential fiber shortening increased during acetate and bicarbonate dialysis (1.47 ± 0.22 to 1.77 + 0.29, p < 0.01; 1.47 ± 0.21 to 1.70 ± 0.22 circ/s, p < 0.01. It is concluded that mild hyperacetatemia does not influence LV contractility and that dialysis-induced changes in serum electrolytes are responsible for the increase in LV contractility during dialysis. However, the pronounced acetate effect on LV preload implies considerable therapeutic implications.