MicroRNAs (miRNAs) are a class of highly conserved, small, noncoding RNAs that play roles in a wide range of biologic processes. Dysregulated miRNA expression has been associated with human cardiovascular disease, and studies using animal models have shown that miRNAs are essential for cardiac development and remodeling. These previously unrecognized small molecules shed new light on the regulatory mechanisms underlying cardiac development and pathology, suggesting the potential importance of miRNAs as diagnostic markers and therapeutic targets for cardiovascular disease.