BACKGROUND: MicroRNAs (miRNAs) are endogenous small RNAs that are 21-25 
nucleotides in length. Recently, plasma miRNAs have been reported to be 
sensitive and specific biomarkers of various tissue injuries and pathological 
conditions. The goal of this study was to assess plasma miRNA profiles and to 
identify plasma miRNAs that are differentially expressed in patients with heart 
failure.
METHODS AND RESULTS: A total of 33 patients with ischemic heart diseases and 17 
asymptomatic controls were recruited. In 10 patients with heart failure, miRNAs 
were assessed at both NYHA IV and III. miRNA array analyses were found to be not 
appropriate for plasma miRNA profiling. The plasma concentrations of 
well-characterized miRNAs (miR-126, 122 and 499) were assessed by a real-time 
reverse transcription-polymerase chain reaction using an artificial small RNA as 
an internal standard. Plasma concentrations of miR-126 were negatively 
correlated with age and logBNP. In 10 patients with heart failure, plasma 
concentrations of miR-126 were up-regulated with improvement of the NYHA class 
from IV to III.
CONCLUSIONS: The plasma concentration of miR-126 was negatively correlated with 
age and NYHA class, and could be a useful biomarker for heart failure.