<jats:sec><jats:title>Aims</jats:title><jats:p>Myostatin inhibits myoblast differentiation/proliferation and may play a role in heart failure (HF) and reverse remodelling after left ventricular assist device (LVAD) support. This study sought to characterize myostatin expression and activation in advanced HF before and after LVAD support.</jats:p></jats:sec><jats:sec><jats:title>Methods and results</jats:title><jats:p>Left ventricular tissue pairs were collected at LVAD implantation (core) and at cardiac transplantation/LVAD explantation in patients with advanced ischaemic (ICM—ischaemic cardiomyopathy) and non‐ischaemic (DCM—dilated cardiomyopathy) HF. Normal cardiac tissue (control) was obtained from hearts not placed for transplantation. Serum was collected independently from patients with stable DCM HF and from healthy controls. Full‐length and cleaved propeptide myostatin levels were quantified by western blot analysis. Dilated cardiomyopathy propeptide levels at core were significantly higher than control and significantly increased after LVAD support. Ischaemic cardiomyopathy propeptide levels were higher than control, but did not change after LVAD support. No changes in full‐length levels were seen. Serum myostatin levels were significantly higher in DCM HF patients than in healthy controls.</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p>This is the first clinical evidence that myostatin activation is increased in HF. Myostatin may affect cardiac hypertrophy and may mediate regression of cellular hypertrophy after mechanical unloading.</jats:p></jats:sec>