Aussie Genetics Fact Sheet: Patent Ductus Arteriosis (PDA) by C.A. Sharp Patent ductus arteriosis (PDA) and the related but less serious condition, ductus diverticulum, are congenital hereditary heart defects which result from the failure of a fetal shunt to resolve, or go away. The purpose of the shunt is to by-pass the lungs. It isn’t necessary for the blood of an unborn animal to circulate through it’s lungs because its oxygen comes from it’s mother. But once it is born and must breathe to obtain oxygen, the blood must pass through the lungs. In ductus diverticulum, the shunt remains but is sealed and does not carry blood, so the blood gets properly oxygenated. However in PDA some portion of the blood still by-passes the lungs resulting in poor oxygenation. Depending on how much blood is missing the lungs, the condition can range from mild to fatal. PDA can easily be detected in young puppies because it causes a heart murmur. Because of this, every Australian Shepherd puppy should be checked for a murmur at a young age (preferably before they leave the breeder’s care.) Not every murmur is a sign of PDA and some are benign and will go away. If a puppy exhibits a murmur, recheck it a few months later. If it fails to go away by the time the dog is six months old or the dog is showing other possible signs of heart trouble, it should be more thoroughly examined to determine the cause. The mode of inheritance for PDA is unknown but probably polygenic (many genes involved.) If a dog is diagnosed with PDA, the cross which produced it should not be repeated. Neither parent, nor any other puppies they have produced should be bred to one-another or to other close relatives. If either parent produces another case of PDA, especially with a mate unrelated to itself or the one with which it previously produced PDA, it should not be bred again. Due to the potentially fatal nature of this defect, if a mating produces multiple affected offspring, the parents and unaffected littermates should be eliminated from breeding.