Heart failure is common, with a prevalence of ∼2% in many parts of the Western World.95 It is characterized by the progressive loss of cardiac systolic and diastolic function, often with acute exacerbations requiring hospitalization, and is associated with severe morbidity and mortality.95 The apelin system has an important role in maintaining cardiac function in health, and is altered in heart failure and may therefore have potential as a beneficial treatment in this setting. Here, APLN is linked to heart failure.