A one-year-old Jack Russell Terrier was referred to Cornell University Hospital for Animals’ Cardiology service for work-up of a murmur and chylothorax after a single incident of respiratory distress. The dog had a heart-murmur diagnosed shortly after birth and did not experience any clinical signs until one year of age. An echocardiogram revealed severe pulmonic stenosis with a right atrium to pulmonary artery pressure gradient of greater than 200mmHg. No cause for the chylothorax was identified. A balloon valvuloplasty was performed and the pressure gradient was reduced to 93mmHg. The patient developed a right atrial thrombus and was placed on clopidogrel. Informal follow up revealed the patient was alive and without clinical signs at six months postoperative.