【Abstract】〓Composed of about 22 nucleotides, microRNA are a class of small, strongly conserved throughout evolution noncoding RNA molecules. MicroRNAs regulate gene expressions by suppressing the translation of the messenger RNA of target genes or by promoting mRNA degradation. The biological function of microRNA is complex and diverse, and has a close relationship with cardiovascular disease, tumor, blood system diseases and liver diseases and so on. Thousands of microRNA to been found, and microRNA21 is a member of the microRNAs. MicroRNA21 is involved in many physiological and pathological processes of cardiovascular system. In recent years, it has been found to play an important role in ischemic heart disease. This review article summarizes the research progress regarding the microRNA21 and its relationship with myocardial ischemic heart disease.