Alpha-smooth muscle actin and serotonin receptors 2A and 2B in dogs with myxomatous mitral valve disease.

•First investigation of serotonin markers in an age-matched dog population grouped according to clinical MMVD status.•A global investigation including the mitral valve, myocardium and serum serotonin.•Analysis of markers in relation to gene expression and protein expression.•Evidence of an association between 5-HT2BR gene expression in the mitral valve and myocardium and clinical MMVD.