During standard haemodialysis, cause of calcium and magnesium insoluble salts formation, the bicarbonate as a buffer has been replaced by the more soluble and stable acetate. But the new and more efficient dialytic systems cause an increase of intradyalitic bicarbonate loss and acetate gain the latter, by a direct calcium binding or by calcium displacement from the active sites, has been believed to be responsible for vasodilatation and myocardial contractility depression. Aim of this study is to verify if the bicarbonate dialysis versus acetate dialysis modifies left ventricular performance, investigated by non invasive tools (systolic time index and echocardiography). This work deals with twelve patients undergoing standard haemodialysis (three times a week) since 28 months on the average. Echocardiographic and systolic time index study was performed before and after the acetate dialysis and before and after the tenth bicarbonate dialysis observing the same interdialytic period. The echo has shown improvement concerning the fractional shortening (P less than 0.025) and the cardiac output (P less than 0.05) and only before the tenth bicarbonate dialysis. Systolic time index data have shown reduction of the ratio PEP/LVET (P less than 0.05) and LVET less negative than after acetate only in the end of the tenth bicarbonate dialysis (P less than 0.05). These results seem point out left ventricular performance improvement in accordance with the decrease of clinical intradialytic (nausea, vomiting, and hypotension) and interdialytic troubles (headache, asthenia and washed-out feeling) probably due to the bicarbonate more effective as a buffer in the acid-base and electrolytic balance.