Introduction:
Melatonin is best known for its influence on circardian physiology. The circulating levels of the hormone vary in a daily cycle, allowing the regulation of the circadian rhythms of several biological functions. Melatonin is now considered as a cardioprotective factor and its secretion might be influenced by the clinical course of CHF.

Objective:
Assessment of the alteration in diurnal and nocturnal melatonin serum levels in patients with chronic heart failure.

Material and Methods:
The study group consisted of 32 patients diagnosed with CHF according to ESC criteria. The study group was divided into two subgroups: patients in NYHA class II (n=21, 8 women) and patients in NYHA class III (n=11, 6 women). In all patients, serum melatonin levels at 02:00 and at 07:00 were determined using competitive enzyme immunoassay technique. High-sensitive C-reactive protein (HsCRP) was determined with nephelometric method.

Results:
Mean hsCRP level was 0.368 (0.195; 0.794) mg/l and 0.54 (0.128; 1.04) mg/l in the group NYHA II and NYHA III patients, respectively; the difference was not statistically significant. NTproBNP levels were higher in NYHA III group than in the group NYHA II [2300 (1509;6317) pg/ml vs 7157 (4155; 13339) pg/ml]; the difference was substantial and approached the level of statistical significance (p=0.057). In both subgroups, higher levels of melatonin at 02:00 than at 07:00 was noticed; however, the differences were not statistically significant (p>0.05). In NYHA III subgroup lower levels of melatonin were observed at both time points; the difference was not statistically significant.

Conclusions:
The study results suggest that in patients with advanced heart failure (NYHA III but not NYHA II), nocturnal melatonin secretion is negatively correlated with NTproBNP.