Heartbase tumor and pericardial effusion in a dog.

Pericardial effusion and congestive heart failure occurred in a ten-year-old male Bouvier des Flandres dog. Signs included weakness, exercise intolerance and ascites. Echocardiography identified a heart base mass as a possible cause of the pericardial effusion. A large quantity (650 mL) of bloody fluid was removed by pericardiocentesis and was characterized at cytology as a nonseptic sanguineous exudate. There was no cytological evidence of neoplasia in the effusate. Pericardiocentesis caused dramatic clinical improvement and resolution of the signs of congestive heart failure. Surgical excision was attempted but the mass could not be resected since it invaded the entire dorsal wall of the right atrium as well as part of the aortic root. The cellular origin of the heartbase tumor could not be determined.