The primary end point will be a change in left ventricular mass index (LVMI) measured in g/m2. As secondary end points the changes in left atrial diameter (LAD), cardiac fibrosis, wall motion abnormalities and left ventricular function, changes in serum FGF 23 and soluble Klotho levels as well as changes in proBNP as well as pre- and postdialysis troponin T (TnT) levels will be determined. Additionally a quantitative analysis of the treatment influence on the individual metabolites of the renin-angiotensin-aldosterone system (RAAS) will be performed using mass spectrometry ("RAAS fingerprint").