The affected patient, a 9.5 year-old male castrated, Standard Poodle, presented to Cornell University’s Emergency Service for treatment of recently diagnosed mitral valve infective endocarditis (IE), lameness and swelling of hind limbs. The patient was already receiving oral antibiotics due to a severe leukocytosis and moderate thrombocytopenia. A urine culture was negative for bacterial growth. On presentation, the patient was febrile, tachycardic and paretic. A new grade III/VI holosystolic murmur was ausculted. Intravenous ampicillin/sulbactam, enrofloxacin and metronidazole were instituted and an echocardiogram confirmed the diagnosis of mitral valve infective endocarditis. Blood was collected for a disseminated intravascular coagulopathy (DIC) panel, complete blood count and chemistry and blood cultures (2 samples, one hr apart). The patient was hospitalized for 6 days, during which time he dramatically improved. He was discharged on long-term oral antibiotics and monitored closely for several months. This paper will discuss the causes, diagnosis and treatment of mitral valve endocarditis.