Myxomatous mitral valve disease (MMVD) in dogs develops over the course of a lifetime. It shares many pathological features with Barlow's disease in humans (MVP, MMVD) including changes in extra-cellular matrix homeostasis and myofibroblast activation. Since canine MMVD is slowly progressive and has a high prevalence it is possible to collect early disease valve samples and to obtain diseased and normal tissue from the same individual. Examining gene changes in the same dog offers a novel approach to identify signalling pathways involved early in the pathogenesis of MMVD. This study aimed primarily to examine the spatial alteration in expression of genes associated with myofibroblast activation and extra-cellular matrix homeostasis in canine MMVD.