Medical management of congestive heart failure in a horse.

A 4-year-old Quarter Horse gelding with atrial fibrillation, mitral regurgitation, and signs of bilateral congestive heart failure was initially treated IV with digoxin and furosemide. After parenteral digitalization, a daily maintenance dose of digoxin was administered orally at a rate of 21.7 micrograms/kg of body weight. At this dosage, a steady-state serum digoxin concentration of 2.3 ng/ml was achieved without clinical signs of toxicosis. The furosemide dosage was decreased and eventually discontinued as clinical improvement occurred. Clinical signs of congestive heart failure were controlled and sinus rhythm was intermittently established, but an unfavorable prognosis was given for future athletic work. After 35 days of therapy, cardiac catheterization was performed and the horse was euthanatized. At necropsy there was marked dilatation of all cardiac chambers, mitral valve fibrosis, and left atrial jet lesions. The response of this patient suggested that orally administered digoxin may be useful in the management of congestive heart failure in selected equine patients.