Takada et al. (2016) treated mice with heart failure with a DPP-IV inhibitor for 4 weeks and found an improvement in peak VO2. This effect may have something to do with GLP-1 because a GLP-1 inhibitor abolished the improvement in VO2peak. Further, they saw improved mitochondrial function and fiber type shifts from IIB to I with DPP-IV inhibition. This same positive effect of DPP-IV inhibition has not been seen in humans with heart failure (Bassi and Fonarow, 2018) and in fact, may be harmful in some people with heart failure (Clifton, 2014; Lourenco et al., 2017). This evidence concerns the gene DPP4 and heart failure.