The let-7 family is the second microRNA found in C. elegans. Recent researches have found it is highly expressed in the cardiovascular system. Studies have revealed the aberrant expression of let-7 members in cardiovascular diseases, such as heart hypertrophy, cardiac fibrosis, dilated cardiomyopathy (DCM), myocardial infarction (MI), arrhythmia, angiogenesis, atherosclerosis, and hypertension. Let-7 also participates in cardiovascular differentiation of embryonic stem cells. TLR4, LOX-1, Bcl-xl and AGO1 are by now the identified target genes of let-7. The circulating let-7b is suspected to be the biomarker of acute MI and let-7i, the biomarker of DCM. Further studies are necessary for identifying the gene targets and signaling pathways of let-7 in cardiovascular diseases. Let-7 might be a potential therapeutic target for cardiovascular diseases. This review focuses on the research progresses regarding the roles of let-7 in cardiovascular development and diseases.