APLN and heart failure: For example, infusion of apelin or ELA in animal models of heart failure has been shown to improve systolic and diastolic function, and reduce detrimental cardiac remodelling.14–16 Apelin receptor signalling has also been implicated in the regulation of both physiological and pathological organ fibrosis,17 and has been shown to reduce detrimental cardiac fibrosis and hypertrophy,18 which is a crucial step in heart failure progression.