Background and Aim: Atrial fibrillation (AF) is one of the most common arrhythmia and is a risk factor for stroke and heart failure. Apelin is a protein with multiple effects on cardiovascular system such as: endothelium-dependent vasodilation, positive inotropy, declining ventricular preload and after-load and increases cardiac contractility. Plasma level of Apelin is a practical tool for evaluating the severity of heart failure, however, it could be a good prognostic factor in Lone AF. Material and methods: In this case-control study, 26 patients with Lone AF and 27 age- and sex- matched controls were enrolled. Meanwhile, the following exclusion criteria were applied at baseline: cardiomyopathy, congestive heart failure, hyperthyroidism, hypertension, coronary artery disease, valvular heart disease, and rheumatic heart disease. Then, 3cc citrated venous blood was obtained and Apelin plasma level was measured with ELISA technique. Results: The study population included 17 males and 9 females with the mean age of 53.1±12.4 years in the LAF and 16 males and 11 females with the mean age of 51.8±8.3 years in the control group. Level of Apelin was not significantly differed between LAF and control group. However, patients aged ³60 years had significantly lower Apelin level when compared with those younger 60 years. Furthermore, gender did not influence the level of Apelin in LAF and control group. Conclusion: Results revealed no reduction in Apelin level of Lone AF group aged <60 years old, but there was a significant reduction in Apelin level among patients aged ³60 years. Hence, Apelin level determination is of low benefit in patients aged <60 years.

Apelin is a recently discovered bioactive peptide, known to be an endogenous high-affinity ligand for the previously orphan G protein-coupled receptor APJ. Apelin/APJ as a novel signaling pathway has been shown to play many crucial roles in cardiovascular function, blood pressure regulation, fluid homeostasis, feeding behavior, obesity, type 2 diabetes mellitus, adipoinsular axis regulation, cell proliferation, angiogenesis, neuroprotection and thermoregulation. This ubiquitous peptide opens a new field of research in biology and medicine. In this regard, the aim of this short review is to compile the evidence for the apelin involvement in modulation of cardiovascular system and introduction of this new peptidic pathway as a useful drug target in the treatment of cardiovascular diseases in future.