Patent Ductus Arteriosus (PDA) in Dogs — A Congenital Heart Defect That Can Usually Be Cured

Patent ductus arteriosus (PDA) is one of the most common congenital heart defects in dogs. The ductus is a blood vessel that connects the aorta and the pulmonary artery before birth; it should close soon afterward. If it stays open, it overloads the heart, and most untreated dogs develop heart failure within their first year or two. When PDA is found early and closed, it is usually cured.

What Is PDA?

Before birth the lungs are not yet working, and the ductus lets blood bypass them. After birth the lungs fill with air, oxygen levels rise and the ductus constricts. In dogs it normally closes within the first week of life. In PDA it stays open. Blood then flows continuously from the aorta into the pulmonary artery, through the lungs and back to the left side of the heart, which becomes overloaded and enlarges. The larger the ductus, the heavier the load.

Predisposed Breeds

PDA has a genetic basis, and about three out of four affected dogs are female. It is most common in small breeds such as the Bichon Frise, Chihuahua, Maltese, Pomeranian, Poodle, Yorkshire Terrier and Shetland Sheepdog, but larger breeds such as the German Shepherd can also be affected. Dogs with PDA should not be bred, even after successful treatment. Their parents, siblings and offspring should also have their hearts checked. PDA occurs in cats as well, but less often.

Signs — What Owners May Notice

Most puppies with PDA seem healthy when the defect is found, and in some dogs it is not detected until adulthood. It is usually discovered at a routine puppy visit, when the vet hears a continuous “machinery murmur.” Sometimes you can feel a buzzing vibration on the left side of the chest. Some puppies are lethargic, tire quickly during play, breathe fast or cough. Fast or labored breathing at rest can be a sign of fluid in the lungs (heart failure) and needs urgent veterinary care.

Reversed PDA — An Important Exception

In a small minority of dogs, a large PDA causes severe high blood pressure in the lungs (pulmonary hypertension), and blood flows the “wrong” way, from the pulmonary artery into the aorta. The typical murmur then disappears. The dog may tire easily or collapse during exercise, with weakness in the hind legs. The vulva or prepuce may look bluish while the gums stay pink. Oxygen-poor blood reaches the kidneys, which then make the body produce too many red blood cells (polycythemia). The ductus must not be closed in these dogs, because closure can cause life-threatening right-sided heart failure. Treatment includes medication such as sildenafil and keeping the red blood cell count down, either by periodically removing blood or with the drug hydroxyurea. The long-term outlook is guarded to poor, although survival varies widely and some dogs live for years.

Treatment

Typical (left-to-right) PDA is treated by closing the ductus. In surgery, the chest is opened and the ductus is tied off. In catheter closure, a device, most often the Amplatz Canine Duct Occluder (ACDO), is passed through a blood vessel, usually in the groin, and seals the ductus from inside. This method is less invasive, but the dog must be big enough for the device, so very small dogs often have surgery. Both methods succeed in most dogs. Deaths are uncommon: in a study of 456 dogs, 2.6% died within three days of the procedure, and in a 2025 study of 200 dogs whose ductus was closed with the ACDO, 0.5% died. The risk is higher if the heart is already markedly enlarged. Medication can stabilize a dog in heart failure before closure but does not cure PDA. Closure is best done soon after diagnosis, ideally before any signs of heart failure.

Diagnosis at Our Clinic

At Eläinklinikka Saari, every puppy’s heart is listened to at its first visit. If we hear a murmur, our veterinarian Leena Sandström can examine the heart with ultrasound (echocardiography) at the clinic. The examination confirms PDA, shows how much strain it causes and checks for other heart defects. We do not close PDAs ourselves: if closure is needed, we refer your dog to a veterinary hospital that performs the procedure.

Prognosis

When the ductus is closed before heart failure develops, the prognosis is excellent and most dogs live a normal lifespan. The heart starts to shrink within a day of closure and usually returns to, or close to, normal size over the following months. A follow-up ultrasound checks that the ductus has sealed completely. Without closure the outlook is poor. In a US study of 520 dogs, the estimated median survival of those with no other heart defect was about 12 years with closure and about 2 years without. Few dogs in the study went untreated, so these figures are rough estimates.

The Most Important Message for Owners

Every puppy’s heart should be listened to at its first veterinary visit. If a murmur is heard, a cardiac ultrasound should be done without delay. PDA can usually be cured — as long as it is found in time. Owners and breeders of predisposed breeds should be especially vigilant.

Sources

1. Merck Veterinary Manual: Cardiac Shunts in Animals (Patent Ductus Arteriosus). merckvetmanual.com
2. Merck Veterinary Manual: Overview of Congenital and Inherited Anomalies of the Cardiovascular System in Animals. merckvetmanual.com
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