CONDITION
Patent Ductus Arteriosus
Patent ductus arteriosus is a condition in which a blood vessel that normally closes soon after birth remains open. Before a puppy or kitten is born, a short vessel called the ductus arteriosus connects two of the large arteries leaving the heart, allowing blood to bypass the lungs while they are not yet functioning. In most animals, this vessel closes within the first few days of life; when it does not, blood continues to flow through it in a pattern that places extra strain on the heart and lungs. Owners most commonly encounter this condition when a murmur is detected during a routine puppy or kitten check, often before any signs are apparent. In some cases, an animal may show reduced energy, slower growth, or changes in breathing pattern as the heart begins to work harder. The condition occurs more frequently in certain breeds, and the severity of signs depends largely on how much blood is moving through the open vessel. This page explores the signals that may bring this condition to attention, the mechanisms by which the open duct affects circulation and heart function, the investigations used to confirm and characterise it, and the range of approaches that exist for managing it.
Why this matters now
Patent ductus arteriosus is a condition present from birth, though the timing of detection varies. The vessel in question is meant to close within the first two to three days of life, and when it remains open the pattern becomes established in the early weeks. Certain breeds appear more frequently in clinical records, including Poodles, German Shepherds, Collies, and Maltese dogs, though the condition can occur in any breed or in cats. The signs, when they appear, often begin to surface in the first few months as the heart adjusts to the altered workload.
The course of this condition depends largely on the volume of blood moving through the open duct. In some animals, the heart compensates for a period and signs remain subtle or absent for weeks or months, even while the heart is already enlarging. Over time, the left side of the heart may begin to enlarge as it works to manage the extra circulation, and fluid can begin to accumulate in the lungs. In dogs with the usual left-to-right form, this progression is the expected course rather than one possibility among several. Without closure, most develop left-sided heart failure, and a majority die before one year of age. Enlargement of the heart becomes less reversible the longer the extra volume continues, which is why closure is generally advised soon after the diagnosis is confirmed, including in puppies that still appear well.
Signals & patterns
Early signals
Murmur detected at routine check
A continuous heart murmur is often the first finding, typically noticed during a puppy or kitten vaccination appointment. The murmur may be audible in a characteristic location on the chest, and the animal may otherwise appear entirely well.
Reduced stamina during play
Some young animals tire more quickly than their littermates during energetic activity. The difference may be subtle at first, noticed as a tendency to rest whilst others continue or a reluctance to sustain vigorous play.
Slower weight gain or growth
Growth can lag behind expected rates, particularly in puppies with larger volumes of diverted blood. The animal may eat normally but fail to match the size or weight of siblings at the same age.
New coughing
A cough may develop as fluid begins to accumulate in the lungs. In a puppy or kitten with a heart murmur, a new cough, particularly alongside faster breathing, can be an early sign of heart failure rather than a routine airway infection, and the two cannot be told apart at home.
Later signals
Increased breathing effort at rest
Breathing may become faster or require visible effort while the animal is resting or asleep. Open-mouth breathing, flared nostrils, an extended neck or reluctance to lie down can accompany it. In a young animal with this condition, these changes can reflect fluid in the lungs (pulmonary oedema) from left-sided heart failure, which can worsen over hours and can be fatal without treatment. The cause of laboured breathing cannot be determined at home.
Exercise intolerance
The animal may stop during walks, choose to lie down rather than move, or show reluctance to engage in activities previously enjoyed. Recovery after exertion may take longer than it once did.
Pale, grey or bluish gums
Pale, grey or bluish (dusky) gums, or colour that is slow to return after gentle pressure, indicate that circulation or oxygen delivery is reduced. In a young animal with this condition they can accompany fluid in the lungs and may precede collapse. In the less common reversed form, the gums may look pink while the lining of the penis, prepuce or vulva looks bluish, because blood low in oxygen passes to the back half of the body. Hind limb weakness on exercise can accompany this, and a murmur may be absent.
Click to read about the biological mechanisms
How this is usually investigated
Investigation typically begins when a heart murmur is detected during routine examination, often in a young puppy or kitten. The character of the murmur—its timing, location, and quality—may suggest the possibility of a patent ductus arteriosus, prompting more detailed assessment. Investigations are then directed at confirming the presence of the open vessel, measuring its size and the volume of blood moving through it, and evaluating the degree to which the heart and lungs have been affected.
Physical examination
Radiography
Echocardiography
Electrocardiography
Blood tests
Options & trade-offs
Management is shaped by the size of the duct, the degree of heart and lung involvement, the age and general health of the animal, and what is practical within the household. For the usual left-to-right duct, closure by surgery or by a catheter-placed device is the approach that changes the long-term outlook, and many dogs with a successful closure go on to a normal or near-normal lifespan. Where the direction of flow has reversed, the position is the opposite. Closing a reversed duct is contraindicated, because the duct is acting as an outlet for high pressure on the right side of the heart, and closure can cause fatal right-sided heart failure.
Surgical ligation
The open duct can be closed by placing ligatures around it during open-chest surgery, physically sealing the vessel. This approach has been used for many decades and can result in resolution of the abnormal flow pattern. The procedure is typically performed by a specialist surgeon and involves a period of hospitalisation and recovery.
Trade-offs: Surgery carries risks associated with general anaesthesia and opening the chest, including bleeding and infection. Recovery takes several weeks, and the success rate depends on the size and accessibility of the duct. The most serious surgical risk is bleeding if the duct tears during dissection, which can be fatal. Ligation can be performed in very small puppies, and it is usually the route taken when the leg arteries are too narrow for a catheter device. Animals already in heart failure are typically stabilised with medication before the procedure.
Interventional catheterisation
A catheter can be threaded through a blood vessel, usually in the leg, and guided into position near the duct under imaging guidance. A device such as a coil or occluder is then deployed to block the flow through the open vessel. This approach avoids opening the chest and typically involves a shorter hospital stay.
Trade-offs: Catheter-based techniques require specialised equipment and training, and access may be limited to referral centres. The artery used for access, usually the femoral artery in the hind leg, has to be large enough for the delivery system, which can rule this approach out in very small puppies. The size and shape of the duct also influence whether a device can be placed successfully, and in some cases complete closure is not achieved. Complications can include device migration or residual flow.
Medical management
Medications can be used to reduce the workload on the heart and manage fluid accumulation in the lungs. Diuretics may be given to decrease lung oedema, and drugs that support heart function or reduce strain on the left ventricle may also be used. This approach does not close the duct but can improve comfort and slow progression.
Trade-offs: Medical management is ongoing and does not alter the underlying anatomy. Signs may improve, but the heart continues to work against the abnormal flow pattern, and progression can still occur. This approach may be chosen when intervention is declined, not feasible, or deferred while the animal is stabilised.
Monitoring without closure
For a left-to-right duct, monitoring alone is uncommon, because most untreated dogs go on to develop heart failure. It is mainly the course taken where flow through the duct has reversed and closure is no longer an option. Management then focuses on the consequences, such as thickening of the blood from a raised red cell count and high pressure in the lung vessels, and can include periodic removal of blood and medication aimed at the lung circulation. Monitoring may also be the course where closure has been declined or is not feasible.
Trade-offs: For a left-to-right duct, this approach avoids the risks and costs of a procedure but leaves the extra volume load in place. Heart enlargement that develops during a period of monitoring may not fully reverse if closure is carried out later, and signs of heart failure, such as faster or effortful breathing at rest, can appear over hours. With a reversed duct, the outlook depends on the degree of disease in the lung vessels, and hind limb weakness or collapse on exercise can occur.
Common misconceptions
"A heart murmur in a puppy always means something serious."
Many puppies have a soft murmur heard only as the heart contracts (a systolic murmur) that is innocent and usually fades by around four to five months of age. The murmur typical of patent ductus arteriosus is different. It is continuous, heard through both contraction and relaxation of the heart, often described as a machinery sound, and loudest high on the left side of the chest. A continuous murmur of this kind is not an innocent finding. The character of a murmur is judged with a stethoscope and often confirmed with echocardiography, and it cannot be assessed at home.
"If the puppy seems well, the duct must be small and harmless."
The correlation between clinical signs and the haemodynamic significance of the duct is not always tight, particularly in young animals whose hearts may compensate for a period. Some animals with relatively large ducts show few outward signs in early life, whilst changes in heart size and function are already underway. The absence of obvious signs does not reliably predict the trajectory.
"Closing the duct will restore the heart to completely normal function."
Successful closure of the duct halts the abnormal flow pattern and can allow the heart to remodel over time, often with marked improvement in size and function. However, the extent of recovery depends on the degree of change that occurred before closure, and some enlargement or functional alteration may persist, particularly if intervention was delayed. Early closure tends to be associated with more complete normalisation.
Related conditions
Ventricular Septal Defect
Ventricular septal defect is another congenital heart condition in which an abnormal opening exists between two chambers of the heart, in this case the ventricles rather than the great vessels. Both conditions create abnormal patterns of blood flow that place extra strain on the heart, and in some animals both defects can occur together.
Atrial Septal Defect
Atrial septal defect shares the category of congenital heart defects that involve abnormal openings or connections, though in this condition the opening sits between the upper chambers rather than in a vessel. Both may be discovered in the same way—through detection of a heart murmur during early life—and both create patterns of altered blood flow that can affect heart function over time.
Pulmonic Stenosis
Pulmonic stenosis is another form of congenital heart disease that can be detected during routine puppy examination. While the underlying anatomy differs—stenosis involves a narrowing rather than a persistent vessel—both conditions increase the work demanded of the heart and may present with similar early signals such as a murmur, exercise intolerance, or slow growth.
Congestive Heart Failure in Dogs
Congestive heart failure can develop as a consequence of patent ductus arteriosus when the abnormal blood flow pattern places prolonged strain on the heart, eventually overwhelming its ability to move blood efficiently. The failure that follows a left-to-right duct is typically left-sided, with fluid accumulating in the lungs (pulmonary oedema) and faster or effortful breathing at rest, and in many untreated dogs it develops within the first year of life.
Pulmonary Hypertension
Pulmonary hypertension is the change that can reverse the direction of flow through a patent ductus arteriosus, rather than a consequence of that reversal. In an uncommon group of animals, pressure in the lung vessels rises above that in the aorta, usually early in life, so that blood low in oxygen passes through the duct to the body, a pattern sometimes called Eisenmenger physiology. Once flow has reversed, closing the duct is contraindicated, as it can cause fatal right-sided heart failure.
Patent ductus arteriosus sits within a broader group of congenital heart conditions, some of which share features such as murmurs or altered heart size but differ in mechanism and outlook. For an animal with a confirmed left-to-right duct, the timing of closure has a large bearing on the result, because a majority of untreated dogs die within the first year and heart enlargement becomes less reversible with time. Where flow has reversed, closure is no longer an option and the focus shifts to managing its consequences. In an animal with this diagnosis, faster or effortful breathing at rest, dusky gums, fainting or collapse can mean fluid in the lungs or failing circulation, which can change over hours.
Last reviewed: 13 September 2026 · Dr Alastair Greenway MRCVS