Pulmonary atresia and ventricular septal defect (PA-VSD) was diagnosed in a 2-year-old castrated male Terrier mix. Transthoracic echocardiography identified a large ventricular septal defect, overriding aorta and severe right ventricular hypertrophy. A main pulmonary artery could not be identified, consistent with pulmonary atresia or persistent truncus arteriosus. Transesophageal echocardiography and angiography confirmed PA-VSD with aortopulmonary collateral circulation arising from the descending thoracic aorta. This case report describes the antemortem diagnosis of the rare congenital defect PA-VSD in an adult dog.