Objectives Apelin, the novel endogenous ligand for the G-protein-coupled receptor APJ, has been observed in many animals and humans studies. It is concluded that it has inotropic effects, hypotension and diuretic properties. The change of apelin in relation to heart failure is still controversial. Our goal was to observe the change of apelin-12 in patients with heart failure (HF). Methods From 2005 to 2006, 81 consecutive patients (46 male and 35 female, mean age 68.5±12.1 years) with heart failure resulting from variable etiologies and 15 healthy controls were included in this study. Plasma concentration of apelin-12 was measured through ELISA on admission. All patients received conven-tional therapy and recorded detailed the clinical condi-tions. Results (1) Plasma concentration of apelin of the controls is lower than the ones of heart failure patients. (2) Plasma concentration of apelin is increased in the early stage and decreased in the advanced period. (3) Apelin is related with variable indexes in the Pearson’s association analysis. Apelin is also changed with the atrium and ventricular’s diameter. Conclusions Plasma concentration of apelin is increased in early stage and decreased in advanced period. The apelin-APJ system might be important in the pathophysiological process of heart failure. And it might be valuable in diagnosis and therapeutic implications in heart failure. Objectives Apelin, the novel endogenous ligand for the G-protein-coupled receptor APJ, has been observed in many animals and humans studies. It is said that it has inotropic effects, hypotension and diuretic properties. The change of apelin in relation to heart failure is still controversial. Our goal was to observe the change of apelin-12 in patients with heart failure (HF). Methods From 2005 to 2006, 81 consecutive patients (46 male and 35 female, mean age 68.5 ± 12.1 years) with heart failure Results from variable etiologies and 15 healthy controls were included in this study. Plasma concentration of apelin-12 was measured through ELISA on admission. All patients received conven-tional therapy and recorded detailed the clinical condi- tions. Results (1) Plasma concentration of apelin of the controls is lower than the ones of heart failure patients. (2) Plasma concentration of apelin is increased in the early stage and decreased in the advanced period. (3) Apelin is related with Apes are also important in the pathophysiology process of heart failure And it might be valuable in diagnosis and therapeutic implications in heart failure.