The leading cause of death for patients with Duchenne muscular dystrophy (DMD), a progressive muscle disease, is heart failure. Prostaglandin (PG) D₂, a physiologically active fatty acid, is synthesized from the precursor PGH₂ by hematopoietic prostaglandin D synthase (HPGDS). Using a DMD animal model (mdx mice), we previously found that HPGDS expression is increased not only in injured muscle but also in the heart. Moreover, HPGDS inhibitors can slow the progression of muscle injury and cardiomyopathy. However, the location of HPGDS in the heart is still unknown. Thus, this study investigated HPGDS expression in autopsy myocardial samples from DMD patients. We confirmed the presence of fibrosis, a characteristic phenotype of DMD, in the autopsy myocardial sections. Additionally, HPGDS was expressed in mast cells, pericytes, and myeloid cells of the myocardial specimens but not in the myocardium. Compared with the non-DMD group, the DMD group showed increased HPGDS expression in mast cells and pericytes. Our findings confirm the possibility of using HPGDS inhibitor therapy to suppress PGD₂ production to treat skeletal muscle disorders and cardiomyopathy. It thus provides significant insights for developing therapeutic drugs for DMD.