CONDITION
Aortic Stenosis
Aortic stenosis is a narrowing of the heart's aortic valve or the region just above or below it, restricting the flow of blood as it leaves the left ventricle and enters the body's main circulation. The narrowing can range from mild to severe, and many affected dogs live without obvious signs for years, whilst others develop limitations in exercise tolerance, episodes of weakness, or collapse. Owners often arrive on this page after a heart murmur has been detected during a routine examination, or because a young dog has shown fatigue or breathlessness during exercise that seems out of proportion to the activity. In some cases the condition is discovered incidentally, in a dog that appears entirely well. This page explores the signals that can accompany aortic stenosis, the structural and functional changes that underlie them, the ways the condition is investigated and graded, and the range of approaches used to manage dogs across the spectrum of severity.
Why this matters now
Aortic stenosis is present from birth, though it may not be detected at first as the heart and surrounding structures continue developing during early life. The condition is inherited in several breeds, including Newfoundlands, Golden Retrievers, Rottweilers, and Boxers. Murmurs may become more apparent as puppies grow, and the fibrous narrowing can progress during the first year of life.
The severity of aortic stenosis varies considerably between individuals. Mild cases may cause minimal clinical effects and remain stable. Moderate to severe stenosis places increasing strain on the heart muscle, which thickens in response to the extra workload. Over time, this can lead to reduced exercise tolerance, abnormal heart rhythms, and in severe cases, sudden collapse or heart failure. The condition may progress during the growth period but typically stabilises thereafter.
Signals & patterns
Early signals
Heart murmur detected on examination
A characteristic murmur heard at the left heart base, often detected during routine puppy examinations.
Subtle exercise intolerance
Affected puppies may lag behind littermates during play or tire more easily than expected.
Weaker femoral pulses
In more severely affected dogs, the pulse felt in the groin (femoral pulse) may be weaker than expected, reflecting reduced blood flow through the narrowed outflow.
Slightly prolonged recovery after activity
Taking longer to return to normal breathing patterns after exercise.
Later signals
Obvious exercise intolerance
Clear reluctance or inability to exercise at expected levels, with rapid fatigue.
Episodes of weakness or collapse
Transient weakness or fainting, particularly during or after exertion, due to abnormal heart rhythms or inadequate cardiac output.
Laboured breathing
Increased respiratory rate or effort, potentially indicating heart failure development.
Sudden death
Some dogs, mainly those with severe narrowing, die suddenly from abnormal heart rhythms, sometimes during or after exertion and sometimes with no earlier signs. In a study of 96 untreated dogs, 21.9% died suddenly, mainly in the first 3 years of life.
Click to read about the biological mechanisms
How this is usually investigated
Diagnosis involves cardiac auscultation followed by imaging to assess the severity of narrowing and its effects on the heart. Comprehensive evaluation helps determine prognosis.
Cardiac auscultation
Echocardiography (cardiac ultrasound)
Electrocardiogram (ECG)
Holter monitoring
Chest radiographs
Options & trade-offs
Management depends on severity and ranges from monitoring to intervention. Treatment aims to reduce cardiac workload and manage complications.
Monitoring without treatment
Regular cardiac assessments to track progression in mild cases.
Trade-offs: Appropriate for dogs with minimal stenosis. Many mild cases live normal lifespans. Requires commitment to periodic reassessment.
Exercise restriction
Limiting strenuous activity to reduce cardiac demands and arrhythmia risk.
Trade-offs: May help reduce risk of collapse or sudden death. Degree of restriction depends on severity. Can affect quality of life.
Beta-blocker medication
Medicines such as atenolol that slow the heart rate and reduce the force of contraction, lowering the heart muscle's oxygen demand. Atenolol is a human medicine, not authorised for dogs in the UK, and is prescribed under the veterinary medicines cascade.
Trade-offs: Used with the aim of reducing heart workload and arrhythmia risk. Does not address the underlying obstruction. A retrospective study of 50 dogs with severe subaortic stenosis found that beta-blocker treatment did not change survival. Regular monitoring needed.
Anti-arrhythmic medications
Drugs to control abnormal heart rhythms when these are documented. Those used in dogs, such as sotalol, are human medicines not authorised for dogs in the UK and are prescribed under the veterinary medicines cascade.
Trade-offs: May reduce risk of arrhythmia-related collapse. Selection depends on arrhythmia type. Not always effective.
Interventional procedures (balloon dilation or surgery)
Procedures to reduce the obstruction, though rarely performed.
Trade-offs: May be considered in severe cases. Requires specialised facilities. Results can be temporary as stenosis may recur. Carries procedural risks.
Common misconceptions
"A loud murmur always means severe disease"
Whilst murmur intensity can relate to severity, the relationship is not absolute. Echocardiography provides accurate assessment of stenosis severity.
"Dogs with heart murmurs should not exercise at all"
Exercise recommendations depend on severity. Dogs with mild stenosis may live normal active lives, whilst those with more significant disease may need restrictions.
"The condition can be completely cured with surgery"
Interventional procedures can reduce obstruction but are rarely curative. The fibrous tissue may reform, and underlying heart changes persist. Medicines may still be used after a procedure to help control heart rhythm and workload.
Related conditions
Dilated Cardiomyopathy in Dogs
Dilated cardiomyopathy is a primary heart muscle disease in dogs, with chamber enlargement and wall thinning, unlike aortic stenosis, which is an outflow obstruction. Both can cause exercise intolerance and murmurs. Both conditions are monitored with similar imaging techniques and can progress to heart failure, though through distinct mechanisms.
Hypertrophic Cardiomyopathy in Cats
Hypertrophic cardiomyopathy in cats shares with aortic stenosis the feature of left ventricular outflow obstruction, though in cats this arises from thickened heart muscle rather than a fibrous ridge below the aortic valve. The functional consequence, restricted blood ejection from the left ventricle, can produce overlapping signs of exercise limitation and murmurs in both species.
Pericardial Effusion
Pericardial effusion can present with similar signs of weakness, collapse, or reduced exercise tolerance, and both conditions may be investigated with echocardiography to assess cardiac structure and function. Distinguishing between outflow obstruction and external cardiac compression often depends on imaging findings rather than clinical signs alone.
Laryngeal Paralysis in Dogs
Laryngeal paralysis can cause exercise intolerance, respiratory noise, and collapse in dogs, and may be considered when aortic stenosis is mild but signs seem disproportionate, or when both conditions coexist in older large-breed dogs. The distinction often rests on the character of breathing sounds and the presence or absence of a cardiac murmur.
Tracheal Collapse
Tracheal collapse can produce coughing, exercise intolerance, and respiratory distress that may overlap with signs attributed to heart disease, although tracheal collapse mainly affects small breeds while subaortic stenosis is mainly a defect of large breeds. Careful assessment of respiratory versus cardiac contributions often involves imaging both the airway and the heart.
Endocarditis
Dogs with subaortic stenosis are at higher risk of infective endocarditis, where the aortic valve damaged by the high-velocity jet becomes infected. It tends to occur later in life and in dogs with mild to moderate narrowing, and can cause fever, lethargy and a change in the murmur.
Noting the breed and any known family history of heart conditions provides relevant background. Observing exercise tolerance compared to other dogs of similar age and breed can help identify subtle changes. Documenting any episodes of weakness, excessive fatigue, or collapse, including what activity preceded them, offers valuable information for cardiac evaluation. A faint or collapse, or fast or laboured breathing at rest, cannot be judged at home in a dog with aortic stenosis, because either can come from a dangerous heart rhythm or from heart failure, and these signs are usually assessed by a vet the same day.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS