A 5-year-old male French Bulldog was referred to the surgery service and the preanaesthetic evaluation was considered within normal limits. Ten days later, the dog was submitted for severe respiratory distress. An intrathoracic mass was observed in the radiographic and ultrasound studies. The owner decided to euthanize the dog. On necropsy, a mass was found expanding the right atrial wall and partially collapsing the right atrium. Histologically, the mass was diagnosed as a primary cardiac fibrosarcoma.

Key words: Cardiac, Dog, Fibrosarcoma