In case of NEK9-knockdown, we observed the development of progressive heart failure with a penetrance of 72 ± 3.5% (Fig. 4A, B) and strongly reduced fractional shortening (FS) of atrium (a) and ventricle (v) at 72 h post fertilization (hpf) (KD-NEK9: aFS: 40.5 ± 2.6%, vFS: 34.4 ± 2.6%; Ctrl: aFS: 60.8 ± 1.3%, vFS: 55.3 ± 0.2%, P < 0.001) (Fig. 4C and Supplementary Movie 1). This evidence concerns the gene NEK9 and heart failure.