The objectives of the study were: (1) the assessment and comparison of the expression of desmin, vimentin, periostin and caspase-3 in the left atrial myocardium in dogs with DCM and MMVD showing severe left atrial enlargement; (2) comparison of those results with the results from a group of dogs without heart disease; (3) the evaluation of the correlation between the expression of the examined proteins and heart remodelling based on the histological examination. Here, DES is linked to familial dilated cardiomyopathy.