Cardiac remodeling is the major pathological change of heart failure. And let‐7 family has been implicated in the development and pathogenesis of cardiovascular diseases. However, the mechanisms underlying let‐7b‐5p‐mediated cellular pathogenesis of cardiac remodeling are not well understood. The present study aimed to explore the effects of let‐7b‐5p on cardiac remodeling and the corresponding regulatory mechanism. In vivo results indicated that cardiac let‐7b‐5p was upregulated in the mouse model of Angiotensin II (Ang II)‐induced cardiac remodeling. Additionally, let‐7b‐5p knockdown ameliorated the effects of Ang II‐induced cardiac remodeling, whereas let‐7b‐5p overexpression facilitated cardiac remodeling. In vitro, let‐7b‐5p mimics induced cardiomyocyte hypertrophy, fibroblast transdifferentiation, and the expression of inflammatory factors in neonatal mouse cardiomyocytes (NMCMs), neonatal mouse cardiac fibroblasts (NMCFs), and bone marrow‐derived macrophages (BMDMs), respectively. Furthermore, let‐7b‐5p exerted its cardiac pro‐remodeling effects at least partially through a small extracellular vesicle (SEV)‐based delivery strategy. We found that let‐7b‐5p was enriched in SEVs derived from Ang II‐treated NMCMs (NMCM‐SEV) but not from Ang II‐treated NMCFs (NMCF‐SEV). Mechanistic analyses revealed that NMCM‐SEV promoted TLR7 and MyD88 expression, which increased NF‐κB phosphorylation levels. Knockdown of let‐7b‐5p, TLR7 or MyD88 in NMCMs, NMCFs, and BMDMs abolished the cardiac pro‐remodeling effects of NMCM‐SEV. These results uncover that let‐7b‐5p‐containing NMCM‐SEVs promote cardiac remodeling via the TLR7/MyD88/NF‐κB pathway, implicating let‐7b‐5p as a potential therapeutic target for heart failure.