The function of APELA (apelin receptor early endogenous ligand, Ensembl gene identifier ENSG00000248329) is as follows. Peptide hormone that functions as endogenous ligand for the G protein-coupled apelin receptor (APLNR/APJ), that plays a role in the regulation of normal cardiovascular function and fluid homeostasis (PubMed:25639753, PubMed:28137936, PubMed:35817871). Functions as a balanced agonist activating both G(i) protein pathway and beta-arrestin pathway of APLNR (PubMed:35817871). Downstream G proteins activation, apelin can inhibit cAMP production and activate key intracellular effectors such as ERKs (PubMed:35817871). On the other hand, APLNR activation induces beta-arrestin recruitment to the membrane leading to desensitization and internalization of the receptor (PubMed:35817871). Required for mesendodermal differentiation, blood vessels formation and heart morphogenesis during early development and for adult cardiovascular homeostasis (PubMed:25639753, PubMed:28137936). Acts as a motogen by promoting mesendodermal cell migration during gastrulation by binding and activating APLNR. Acts as an early embryonic regulator of cellular movement with a role in migration and development of cardiac progenitor cells. May act as a chemoattractant for the activation of angioblast migration toward the embryonic midline, i.e. the position of the future vessel formation, during vasculogenesis. Positively regulates sinus venosus (SV)-derived endothelial cells migration into the developing heart to promote coronary blood vessel sprouting. Plays a role in placental vascular development; promotes placental trophoblast invasion and spiral artery remodeling in the uterus. Involved in the regulation of maternal cardiovascular homeostasis to prevent gestational hypertension and for potent cardioprotective functions during heart failure. Mediates myocardial contractility in an ERK1/2-dependent manner (By similarity). {ECO:0000250|UniProtKB:P0DMC2, ECO:0000250|UniProtKB:P0DMC4, ECO:0000250|UniProtKB:P0DP76, ECO:0000269|PubMed:25639753, ECO:0000269|PubMed:28137936, ECO:0000269|PubMed:35817871}.