A 4-year-old intact male Shih Tzu dog (weighing 5 kg), was presented with signs of severe dyspnea, exercise intolerance and cyanosis. Diagnostic studies suggested a reverse patent ductus arteriosus (rPDA) with pneumonia. Despite emergency treatments with oxygen, diuretics, antibiotics and medical therapy for hyperkalemia, the dog died of ventricular fibrillation from hyperkalemia and dehydration. Necropsy revealed the rPDA with a marked descending aortic dilation and abnormally arisen left common carotid artery.