Background: Apelin is a potent endogenous inotropic peptide with a major role in counteracting the aldosterone and angiotensin II and their negative effects on the cardiovascular system. The exact role of apelin in the pathophysiology of this disease is not well understood. We aimed to investigate the possible associations of apelin-13with clinical and paraclinical characteristics in HF patients as well as studying its dynamics during the course of the heart failure. Method: We performed a prospective observational cohort single-center study. We compared the baseline serum levels of apelin-13 and NT-proBNP level in 53 heart failure patients (acute heart failure, chronic compensated heart failure and chronic decompensated heart failure). We divided the patients according to the apelin-13 level: above and below the median, and we analyzed the relationship between serum apelin-13 and the clinical, echocardiographic, electrocardiographic and biological parameters. Twenty patients were followed-up (after an average time interval of 9 months), investigating the same parameters. Results: The median of apelin-13 was 495pg/mL . We found strong, negative correlation between the serum levels of apelin-13 and p<0.001). For the reassessed patients the median apelin level was significantly higher at follow-up (460 pg/mL, IQR 342-871 pg/mL) as compared with the baseline level (395 pg/mL, IQR 270-603 pg/mL), p=0.019, and maintained the negative correlation with p<0.001