A 4-years-old golden retriever was presented to our hospital for respiratory distress. Mitral stenosis was diagnosed by echocardiographic findings of doming of the mitral valve leaflets, increased transmitral flow velocity, and decreased mitral valve area. Pleural effusion, atrial fibrillation-flutter and paroxysmal ventricular tachycardia were also observed by electrocardiography and radiography. Medical treatment was selected over surgery per owner preference. Oral administrations of pimobendan, carvedilol, torsemide, and mexiletine hydrochloride were initiated. In previous reports, 50% of dogs with mitral stenosis treated with medications died or were euthanized within one year. Follow-up echocardiographic and electrocardiographic examinations were performed periodically (i.e. every week or every 3 months). Medication dosages were adjusted based on the results of these follow-up examinations. The dog remained clinically stable without recurrence of pleural effusion and died unexpectedly from an unknown cause 866 days after initial presentation.