MicroRNAs (miRs) are small, noncoding RNAs that posttranscriptionally control gene expression by inhibiting protein translation or inducing target mRNA destabilization. Besides their intracellular function, recent studies demonstrate that miRs can be exported or released by cells and circulate with the blood in a remarkably stable form. The discovery of circulating miRs opens up intriguing possibilities to use the circulating miR patterns as biomarker for cardiovascular diseases. Cardiac injury as it occurs after acute myocardial infarction increases the circulating levels of several myocardial-derived miRs (eg, miR-1, miR-133, miR-499, miR-208), whereas patients with coronary artery disease or diabetes showed reduced levels of endothelial-enriched miRs, such as miR-126. This review article summarizes the current clinical and experimental studies addressing the role of circulating miRs as a diagnostic or prognostic biomarker in cardiovascular disease. In addition, the mechanisms by which miRs are released and their putative function as long-distance communicators are discussed.