microRNAs (miRNAs) are a class of small non-coding RNA molecules consisting of 19–22 nucleotides that play an important role in a variety of biological processes, including development, differentiation, apoptosis, cell proliferation and cellular senescence. A growing body of evidence suggests that miRNAs are aberrantly expressed in human cardiac diseases and they play a significant role in the initiation and development. Recently, studies revealed that microRNA-1 (miR-1) was frequently downregulated in various types of cardiac diseases. Here we review recent findings on the aberrant expression and functional significance of miR-1.