A 4 month old American Bulldog presented for episodic syncope and cyanosis. On physical examination, a grade 5/6 left systolic heart murmur, cyanotic mucous membranes, respiratory distress, and poor body condition (BCS 3/9) were noted. Bloodwork revealed polycythemia. Echocardiography definitively diagnosed Tetralogy ofFallot (TOF), an embryologic defect consisting ofright ventricular (RV) outflow obstruction, dextro-positioned aorta, ventricular septa! defect, and RV hypertrophy. TOF patients suffer from hypoxemia due to deoxygenated blood from the RV shunting through the oven-iding aorta, as well as from decreased blood flow from the right ventricle to the lungs secondary to RV outflow tract obstruction. The owner elected for surgical palliation. A modified Blalock Taussig shunt procedure was performed successfully, but the patient developed acute respiratory distress postoperatively and was euthanized. Necropsy identified no gross thrombi. The lungs were congested, edematous, and atelectatic; the patient's acute respiratory distress was attributed to pulmonary over-circulation and acute pulmonary edema. These complications may have been improved via addition of positive pressure ventilation, diuretics, positive inotropes, or preferential pulmonary vasodilation.