STX12 and heart failure: In contrast, Stx12‐cKO mice had an EF% value of 47.4 ± 7.5% (t‐test, p = 0.0006), and an FS% value of 23.4 ± 4.2% (t‐test, p = 0.0004) (data in mean ± SD), indicating the occurrence of heart failure (Figure 2g,h,j).