To determine the impact of Kdm4a deficiency on cardiac fibrosis after MI, AAV9 vector containing the shKdm4a gene with the fibroblast‐specific Postn promoter (AAV9‐Postn‐shKdm4a) was delivered into the myocardial tissue of adult mice to knock down Kdm4a, and AAV9‐Postn‐shNC served as the control. The gene discussed is KDM4A; the disease is myocardial infarction.