A 6-month-old, intacted male dog was admitted to Seoul Animal Medical Center. The referring veterinarian suspected that the patient might have congenital cardiac problem. It was diagnosed with patent ductus arteriosus(PDA) based on the physical examination, auscultation, radiography, electrocardiography and ultrasonogrphy. After surgical ductus closure, there were improved clinical conditions through by alleviation of atrial fibrilation and left heart enlargement.