To investigate the effects of levosimendan, a positive inotropic agent, on the new heart failure markers immunoglobulin free light chains kappa and lambda (FLC-kappa and FLC-lambda) in decompensated chronic heart failure (HF), 59 patients with New York Heart Association (NYHA) class III-IV HF were enrolled. Patients were randomized into levosimendan (n = 31) and standard HF treatment (n = 29) groups. Serum FLC-kappa and FLC-lambda, brain natriuretic peptide (BNP), and ejection fraction (EF) were measured before treatment and on the 5th day of treatment initiation. Forty-two percent of subjects were females (n = 25) and overall mean age was 64.1 +/- 10.7 years. FLC-kappa (P < 0.05) and FLC-lambda (P < 0.05) were significantly decreased in the levosimendan group compared to baseline, but no difference in either marker in the standard treatment group was observed. Pre- and post-treatment FLC-kappa/FLC-lambda ratios in both groups were similar, whereas FLC-kappa and FLC-lambda levels and the FLC-kappa/FLC-lambda ratio showed no significant correlation with NYHA class, brain natriuretic peptide (BNP) and ejection fraction (EF) levels; and BNP and EF changes after the treatment. Symptomatic improvement in the levosimendan group according to the NYHA class was significantly better than in the standard treatment group (P = 0.044). While 55.2% of patients in the levosimendan group showed a 1-degree shift to lower NYHA classes, 10.3% showed a 2-degree decrease. In conclusion, levosimendan caused short-term hemodynamic and symptomatic improvements, with a more pronounced decrease in FLC levels in patients with advanced decompensated HF.