Cardiac aging and cardiac senescence-associated cardiovascular diseases continue to be a serious problem that increases the social burden. Revealing the molecular mechanisms of cardiac aging and cardiac senescence-associated cardiovascular diseases provides a new opinion for the early diagnosis and treatment of delaying aging and diseases. A microRNA (miRNA) is a small single-stranded non-coding RNA molecule that has been found to be involved in the regulation of gene expression at the post-transcriptional level. This paper focuses on the structure and function of miRNA, and its regulatory effects on the characteristics and molecular mechanisms of aging hearts and on age-related cardiovascular diseases.