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.