Pericardial effusion was observed in a 10-year-old Chihuahua diagnosed with myxomatous mitral valve disease. The dog did not have clinical traits related to cardiac tamponade. The dog proceeded to mitral valve repair, and pericardial fluid was removed on incision of the pericardial sac. As the fluid was removed, an increase in ambulatory blood pressure was observed. This report indicates that removal of pericardial effusion may be considered in dogs with mitral valve disease to restore cardiac function, even if cardiac output is not apparently impaired.