MicroRNAs (miRNAs) are a group of newly discovered small RNAs, non-coding, which 
represent one of the most exciting areas of modern medical science as they 
modulate a huge and complex regulatory network of gene expression. Lines of 
evidence have recently suggested that miRNAs play a key role in the pathogenesis 
of heart failure. Some miRNAs highly expressed in the heart, such as miR-1, 
miR-133 and miR-208, are strongly associated with the development of cardiac 
hypertrophy, while the exact role of miR-21 in the cardiovascular system remains 
controversial. Serum levels of circulating miRNAs such as miR-423-5p are being 
evaluated as potential biomarkers in the diagnosis and prognosis of heart 
failure. On the other hand, the manipulation of levels of miRNAs using 
techniques such as mimicking the miRNAs (miRmimics) and antagonistic miRNAs 
(antagomiRs) is making increasingly evident the enormous potential of miRNAs as 
promising therapeutic strategies in heart failure.