Furthermore, consistent with heart failure with preserved ejection fraction (HFpEF) phenotype in which CM contraction defects coexist with the relaxation impairment (Methawasin et al., 2016; Primessnig et al., 2016; Schiattarella et al., 2019), the auxotonic contraction indexed by the SL shortening as well as the SL shortening velocities are also significantly decreased in CMs from CM-specific Efnb1 KO compared to WT CMs (Figure 6C). Here, EFNB1 is linked to heart failure.