Mitral valve endocardiosis (MVE) is the single most common acquired cardiac disease of dogs and is characterized by myxomatous degeneration of the mitral heart valve. The disease is highly age-related and breed specific, but can be seen in any aged dog (Beardow & Buchanan, 1993). Much is known about the clinical features of canine MVE, its diagnosis and management, but little is known about the etiopathogenesis. We have previously hypothesized that it is alteration in the function of the valvular interstitial cell that precipitates the myxomatous degeneration characteristic of the disease, and have shown this to be the case on electron microscopy (Black et al, 2005) and by immunophenotyping (data in preparation for publication). To investigate this phenomenon of interstitial cell phenotypic change further and to attempt to identify the functional consequences, we intend to use proteomics, namely 2-dimensional gel electrophoresis, to identify potential proteins of interest. From these data, in future studies we would use RT-PCR to identify differential gene expressions and identify potential genes of interest.