Primary and secondary cardiac tumours are extremely rare in humans and domestic animals. This case describes the gross, light microscopical and immunohistochemical examination of a cardiac myxoma arising from the tricuspid valve in a 13-year-old female terrier dog. Clinically, long-term respiratory distress, progressive ascites, fatigue and exercise intolerance were observed in the animal. At necropsy, the right ventricular chamber was mildly dilated and a soft, whitish mass, 0.7 x 1.5 x 2.1 cm in size was observed arising from the ventricular surface of the septal leaflet of the tricuspid valve of the heart. Histologically, the mass was composed of a faintly eosinophilic myxoid matrix and spindle shaped fibroblast-like cells with elongated nuclei and stellate cells. The extracellular matrix was stained with periodic acid Schiff and alcian blue and the tumour cells were reactive with anti-vimentin and anti-alpha-sarcomeric actin antibodies. The authors believe that this is the first detailed description of a myxoma in this breed.