The purpose of the present invention is to provide a therapeutic agent for dilated cardiomyopathy disease which produces excellent effects in the treatment of dilated cardiomyopathy (DCM) and provides a given benefit to a large number of patients. The present invention is a therapeutic agent for dilated cardiomyopathy comprising at least one selected from the group consisting of mesenchymal stem cell and microparticles derived from the mesenchymal stem cell. It is preferable that the mesenchymal stem cell is a cell having the ability to contain or secrete microparticles, that the microparticles have an average particle size of 1000 nm or less, and that they are exosomes.