The Apelin Receptor (APJ) is a member of the G protein-coupled receptor (GPCR) family, featuring seven transmembrane domains. APJ primarily binds to its endogenous ligand, apelin, and participates in various physiological processes, including cardiovascular regulation, electrolyte balance, and energy metabolism. APJ is expressed in tissues such as the heart, blood vessels, kidneys, and central nervous system. Activation of APJ regulates intracellular signaling through cAMP and calcium ion signaling pathways. The tissue-specific expression and mutations of the APJ gene are associated with the development and progression of various diseases, including cardiovascular diseases, metabolic disorders, and neurodegenerative diseases.