Left-to-right shunts include patent ductus arteriosus Patent Ductus Arteriosus in Animals Patent ductus arteriosus (PDA) is a common congenital defect of dogs, and it occurs less commonly in cats. Persistent flow through the ductus leads to excess blood flow (volume overload) to... read more , ventricular septal defects Ventricular Septal Defects in Animals Ventricular septal defect is a common congenital defect of cats and also occurs in dogs and can vary in location and size. Most defects are small enough to restrict significant shunting between... read more , and atrial septal defects Atrial Septal Defects in Animals Atrial septal defect is an uncommon congenital defect of dogs and cats. The mid-septal location (secundum-type) is most common. Small defects may be hemodynamically insignificant and require... read more .