MicroRNAs (miRNAs) are emerging as crucial regulators of cardiovascular development and disease. MiRNAs modulate the expression of multiple messenger RNAs with related functions, thereby controlling complex biological processes. In cardiovascular biology, miRNAs play a 'fine-tuning' role in development and tissue homeostasis, and their functions become more pronounced under stress conditions. Specific patterns of miRNA expression correlate with different cardiovascular disorders, and gain- and loss-of-function studies in mice have revealed both pathogenic and protective roles for miRNAs. The ability to manipulate individual miRNAs in vivo using oligonucleotide-based inhibitors or mimics opens up new possibilities for therapeutic interventions in cardiovascular diseases. This review discusses the biology and mechanisms of action of miRNAs in the cardiovascular system and considers the opportunities and challenges for therapeutic modulation of miRNAs in cardiovascular disease.MicroRNAs (miRNAs) are emerging as crucial regulators of cardiovascular development and disease. MiRNAs modulate the expression of multiple messenger RNAs with related functions, thereby controlling complex biological processes. In cardiovascular biology, miRNAs play a 'fine-tuning' role in development and tissue homeostasis, and their functions become more pronounced under stress conditions. Specific patterns of miRNA expression correlate with different cardiovascular disorders, and gain- and loss-of-function studies in mice have revealed both pathogenic and protective roles for miRNAs. The ability to manipulate individual miRNAs in vivo using oligonucleotide-based inhibitors or mimics opens up new possibilities for therapeutic interventions in cardiovascular diseases. This review discusses the biology and mechanisms of action of miRNAs in the cardiovascular system and considers the opportunities and challenges for therapeutic modulation of miRNAs in cardiovascular disease.