Finally, late apelin receptor knockdown in 3D EHTs was found to have detrimental effects on contractile properties, reducing contractility and increasing stiffness compared with control, similar to genetic disruption of apln in mice.2 Our results support the role of apelin signalling in heart contractility, and the link between reduced apelin signalling and the decreased contractile performance observed in heart failure patients.44 Here, APLN is linked to heart failure.