Histological evidence of myxomatous tissue in a Labrador puppy with pulmonic stenosis and tricuspid valve dysplasia.

A six-week-old Labrador retriever was presented for lethargy and anorexia, revealing a systolic heart murmur. Tricuspid valve dysplasia involving the whole tricuspid valve apparatus and the right ventricular wall was found, and an additional pulmonic stenosis was present. Histopathological examination of the tricuspid and pulmonary leaflets highlighted an unusual myxomatous mesenchymal component, interpreted as being of ontogenetic origin.