This is in contrast to the more favorable effect of inhibiting the entire miR-34 family in the pressure overload mouse model in our previous report. As miRNAs target several hundred mRNAs, it is possible that other targets could contribute to the modest cardiac benefit in the moderate model of pressure overload with LNA-antimiR-34a treatment. Finally, inhibition of miR-34a was not protective in a severe model of pressure overload since treatment with LNA-antimiR-34a did not attenuate LV remodeling, improve cardiac function or cardiac stress gene expression, and fibrosis. This finding is consistent with our previous report in which inhibition of miR-34a did not prevent LV remodeling or improve cardiac function following chronic MI. Collectively, these studies suggest that inhibition of miR-34a provides some benefit in an acute setting of cardiac stress or conditions with moderate pathology, but not in chronic or severe settings. A possible explanation for the reduced Butylhydroxyanisole capacity of LNAantimiR-34a to provide protection in chronic or severe settings of cardiac pathology may be due to increased expression of two other miR-34-family members, miR-34b and miR-34c. We have previously shown that LNA-antimiR-34a does not inhibit miR-34b and miR34c, which were both elevated in the TAC severe model in this study. Interestingly, miR-34a was elevated in the hearts of the TAC moderate but not TAC severe model. Thus, this could explain why pharmacologic inhibition was not effective in the TAC severe model, and only partially protective in the TAC moderate model of pressure overload, which had increased levels of all miR-34 family members. miRNA-based therapies are advancing at a rapid rate, with successful completion of phase 1 and phase 2 clinical trials of Santaris Pharma’s LNA-modified antimiR, miravirsen, targeting miR-122 for the treatment of hepatitis C virus infection. Thus, there is great enthusiasm for the development of miRNA-based therapies for cardiovascular disease. The different degrees of efficacy upon inhibition of miR-34a in different cardiac disease models highlights the importance of assessing therapeutic targeting of candidate miRNAs over a broad spectrum of cardiac conditions, as some miRNAs may be more effective than others under particular settings. In recognition that cardiovascular disease and cardiac remodeling is associated with simultaneous dysregulation of several miRNAs or miRNA families, tiny 8-mer seed-targeting LNA-antimiRs could provide an advantage by simultaneous inhibition of entire miRNA seed families. The current study and our previous work highlight a different therapeutic benefit of inhibiting a single miRNA or a miRNA family in moderate and severe models of sustained cardiac stress. Greater therapeutic benefit of inhibiting the entire miR-34 family may be related to the regulation of more target genes. As shown by miRNA target prediction databases based on different algorithms, the miR-34 family is D-Pantothenic acid sodium predicted to repress 24�C40% or 31�C55% more mRNAs than miR-34a alone. Thus, targeting miRNA families may be able to regulate multiple additional biological networks. However, this may have both favorable and unfavorable consequences, and the potential off-target effects must be carefully assessed when developing miRNA therapeutics. Although there are several advantages of developing miRNAbased therapeutics, many miRNAs are ubiquitously expressed and miRNA-based therapeutics are taken up by various organs upon systemic delivery, making clinical intervention complex.