A 15-year-old, neutered male, Shih-Tzu, was presented at the Chonnam National Veterinary Medical Teaching Hospital for evaluation of acute onset of persistent coughing, exercise intolerance, and abnormal heart sound. On thoracic auscultation, a split-second heart sound and a wheezing sound were detected on both sides of the chest walls. On physical examination, the dog's body condition score (BCS) was 7/9, and had stenotic nares. Thoracic radiographs revealed right-sided enlargement of the cardiac silhouette (vertebral heart score (VHS) 11.2; reference interval = 8.9-10.1), mild main pulmonary artery (MPA) bulging, mild interstitial infiltration, and hepatomegaly. The electrocardiogram showed right axis deviation, suggesting right ventricular hypertrophy. The echocardiographic study showed moderate pulmonary hypertension and moderate tricuspid regurgitation. There were no findings of a tracheobronchial disease, pulmonary thromboembolism, congenital shunt, left heart disease, or parasitic disease. Based on clinical signs and diagnostic findings, the dog was diagnosed with pulmonary hypertension secondary to brachycephalic syndrome. To rectify respiratory exacerbating factors, the dog was recommended weight control by restricting dietary intake and managing concurrent Cushing's syndrome. Treatments included sildenafil, pimobendan, furosemide, and ramipril. After five months of taking medications and weight control, the severity of pulmonary hypertension improved from moderate to mild. The clinical signs of the patient, including coughing and exercise intolerance, improved a lot. For 5 months of follow-up, the patient has not reported further recurrence of respiratory distress.

A 2-year-old, spayed female, American shorthair cat presented with acute weight loss, tachypnea, and dyspnea. The cat had grade V holosystolic murmur and systemic hypotension. Echocardiography showed a 9 mm defect in the ventricular septum, left-to-right dominant bi-directional shunt, right ventricular hypertrophy, pulmonary stenosis, pulmonary hypertension, and overriding aorta. The cat was diagnosed with a Tetralogy of Fallot. The cat was treated with furosemide, pimobendan, ramipril, and sildenafil. Treatment reduced pulmonary infiltration, pulmonary vessel enlargement, and main pulmonary artery bulging. However, right-to-left flow increased over time and right ventricular outflow tract velocity was elevated. Currently, the patient has maintained an improved state for 1 year. This case report described a severe inherited feline Tetralogy of Fallot case that was successfully managed for a long time.