Volume overload is a leading risk factor for death and cardiovascular events in end stage renal disease patients maintained on chronic dialysis, particularly in those with myocardial ischemia and heart failure which represent a substantial fraction of this population. Early identification of volume overload may prevent cardiovascular sequel in these patients but clinical signs of volume expansion are unsatisfactory to reliably identify patients at risk and to monitor them over time. On the other hand, however reliable, standard techniques for measuring extracellular or circulating (blood) volume do not convey information on fundamental heart function parameters that determine the individual haemodynamic tolerance to volume excess and the response to ultrafiltration, i.e. left ventricular (LV) filling pressure and LV function.