In addition, species-specific differences in MYOCD requirements for postnatal LV-remodeling, in pigs as compared to mice, could not be excluded, although the underlying mechanisms remain elusive at present. Distinct splice variants of myocd were reported to be expressed in mammalian heart with the myocd B transcript being more abundant in pig ventricular myocardium. In this work, a pool of potential sh-RNAs complementary to different regions of the porcine myocd-B mRNA was generated, and after validation in three distinct experimental setups, the sh-interfering RNA1554 was chosen as the most promising sequence for silencing myocd in DHF, because it effectively targets the endogenous pool of myocd-A/B mRNAs in both pig aortic SMcells in vitro and normal piglet LV-myocardium in vivo. We explored the potential role of myocd inhibition in the piglet heart during HF progression by direct delivery of the myocd-specific silencing plasmid into failing LV-myocardium. Comparative analysis of gene expression and functional consequences of myocd silencing at different time intervals revealed the following noteworthy observations: the early moderate inhibition of endogenous myocd expression attenuated expression of SM-marker genes in failing LV-myocardium, this decrease of MYOCD signaling activity in failing myocardium to the level comparable with that in non-failing animals resulted in improvement of impaired Reversine diastolic function and amelioration of myocardial ischemic conditions, the posterior restoration of elevated myocd expression led to HhAntag691 activation of myocd-dependent SM-marker genes in failing LV-myocardium associated with a return to altered diastolic function, and the transient inhibition of MYOCD signaling at advanced stages of DHF delayed the progression of diastolic dysfunction and extended the survival of failing piglets. In rats, myocardial ischemia and bradycardia are two ECGmanifestations of the acute Dox-induced cardiotoxicity, embodied with decreased heart rhythm. In our model of Dox-induced DHF, myocd targeting was associated with amelioration of such ECG-manifestations suggesting an involvement of MYOCD signaling in the regulation of cardiac function. It is not unreasonable to suggest that impaired diastolic function in Dox-treated piglets is conditioned, at least in part, by overexpression of SM-marker genes in failing myocardium. The induction of these SM-marker genes seems not to be associated with activation of srf expression because srf transcript levels were not changed in failing as compared to non-failing piglet myocardium. Thus, it is tempting to speculate that the activation of SM-marker genes in DHF myocardium can be attributed, at least in part, to selective upregulation of MYOCD. In cardiomyocytes, the level and functional activity of MYOCD is regulated by a balance of positive and negative factors.