Western blot analysis revealed that while the relative levels of MMP9, MMP2, and α-SMA expression in heart tissues of the DCM group of rats were significantly higher than that in the NC group, the levels of MMP2 and α-SMA, but not MMP9, were significantly reduced in the rats receiving two-dose hUCMSCs, particularly in those with IDO-OE hUCMSCs (Fig. 6D–E). Here, IDO1 is linked to familial dilated cardiomyopathy.