CONDITION
Pulmonary Hypertension
Pulmonary hypertension describes sustained elevation of blood pressure within the vessels that carry blood from the heart to the lungs. This increased resistance can develop when underlying disease narrows or stiffens those vessels, or when the heart's left side struggles to receive blood efficiently, causing pressure to build backwards through the lungs. Owners often arrive at this topic after their dog has shown reduced tolerance for activity, episodes of breathlessness, or fainting, particularly during excitement or exertion. Cats may become quieter, breathe more rapidly at rest, or show reluctance to move. In many cases, pulmonary hypertension is discovered during investigation of a heart murmur, chronic cough, or known lung condition. It is not a disease in isolation—it tends to arise secondary to problems elsewhere in the heart or lungs. This page explores the signs an owner may observe, the mechanisms that raise pressure in the pulmonary circulation, the diagnostic steps used to confirm and measure it, and the range of approaches used to address both the elevated pressure and the conditions that drive it.
Why this matters now
Pulmonary hypertension can appear at any life stage, though it is often recognised in middle-aged to older animals when underlying heart or lung conditions have had time to develop. Dogs with certain heart valve changes or chronic respiratory disease may be at higher risk, as can cats with congenital heart defects or chronic lung inflammation. In the UK, left-sided heart disease and long-standing lung conditions are the most common preceding factors; heartworm infection is not endemic in Britain and is only relevant in dogs that have travelled to or been imported from endemic regions such as southern or eastern Europe.
The condition tends to evolve gradually, with the right side of the heart working harder over weeks to months as pressure in the lung vessels rises. Some animals show early, subtle changes in stamina or breathing rate that owners may attribute to ageing or reduced fitness. Others remain relatively steady for a period before signs become more obvious, and the pace of change can vary considerably depending on the underlying cause and how the individual heart responds to the added workload.
Signals & patterns
Early signals
Reduced exercise tolerance
An owner may notice their dog or cat tires more quickly during walks or play, choosing to stop sooner or needing longer to recover. This can be gradual enough that it is mistaken for normal ageing or a temporary loss of fitness.
Faster breathing at rest
Respiratory rate may increase even when the animal is lying quietly, though the change can be subtle and may only become apparent when counted over a minute. The breathing itself often remains comfortable in the early stages.
Occasional coughing
Some animals develop a sporadic cough, particularly after exertion or excitement. The cough may be soft or dry and can be mistaken for clearing the throat or a mild irritation.
Reluctance to lie flat
A dog or cat may begin to prefer sitting or resting with the chest slightly elevated, which can make breathing feel easier when pressure in the lung circulation is rising. This preference may be intermittent at first.
Later signals
Laboured or open-mouth breathing
Breathing may become visibly more effortful, with the chest and abdomen moving more noticeably, and cats in particular may begin to pant or breathe with the mouth open. This typically reflects increasing difficulty moving blood through the lungs and reduced oxygen delivery.
Episodes of weakness or collapse
Some animals experience brief episodes where they appear unsteady, wobbly, or lose consciousness for a few seconds, often following activity. These events can occur when the heart is unable to maintain adequate blood flow to the brain under increased demand.
Fluid accumulation in the abdomen
The abdomen may gradually enlarge as fluid builds up, a consequence of the right side of the heart struggling to move blood forward and pressure backing up into the veins that drain the liver and intestines. Owners may notice the belly appears swollen or the animal's shape has changed.
Click to read about the biological mechanisms
How this is usually investigated
Investigation typically begins with a clinical examination, listening for heart murmurs or abnormal lung sounds and checking for signs of fluid accumulation or reduced oxygen levels. When pulmonary hypertension is suspected, imaging of the heart becomes central to the picture, allowing measurement of pressures and assessment of how the right heart is coping. Additional tests may be arranged to identify underlying conditions that could be driving the vascular changes, such as chronic lung disease, left-sided heart problems, or clotting abnormalities.
Echocardiography
Radiography
Blood pressure measurement
Chemistry panel
Computed tomography (CT)
Options & trade-offs
Management typically combines approaches aimed at lowering pulmonary vascular resistance, supporting the right heart's workload, and addressing any underlying conditions that may be sustaining the elevated pressures. The combination chosen depends on the severity of signs, the presence of other heart or lung disease, and what proves practical for a given household. Different animals and owners find different balances workable, and what suits one situation may be less feasible in another.
Pulmonary vasodilator medication
Drugs such as sildenafil work by relaxing the smooth muscle in pulmonary artery walls, widening the vessels and reducing the resistance against which the right heart pumps. The medication is usually given two or three times daily, and some animals show reduced breathing effort or improved exercise tolerance within days to weeks. The effect tends to be more pronounced when vascular constriction, rather than structural remodelling or clotting, is the dominant mechanism.
Trade-offs: Sildenafil can lower systemic blood pressure in some individuals, occasionally causing lethargy or weakness, and the frequency of dosing may be challenging in cats or in households with complex schedules. The medication does not reverse vessel wall thickening that has already occurred, and response varies between animals.
Diuretic therapy
Diuretics such as furosemide reduce fluid accumulation in the lungs or abdomen by increasing urine output, which can ease breathing effort when congestion is present. The dose is often adjusted over time, guided by breathing rate at rest, weight, and signs of dehydration or changes in kidney function.
Trade-offs: Frequent urination can be inconvenient, particularly overnight or in animals with limited mobility, and overuse can lead to dehydration, electrolyte imbalances, or worsening kidney function. Diuretics address the consequences of fluid backup rather than the underlying vascular resistance.
Management of underlying conditions
When pulmonary hypertension arises secondary to another process, efforts to stabilise or slow that condition can reduce the stimulus for ongoing vascular changes. This may involve medication for left-sided heart disease such as mitral valve disease, inhaled or systemic drugs for chronic airway inflammation, or anticoagulant therapy if thromboembolic disease is suspected. Heartworm infection is not endemic in the UK and is only a relevant consideration in dogs that have travelled to or been imported from endemic regions such as southern or eastern Europe; in dogs with no such travel history, left-sided heart disease and chronic lung conditions are far more common drivers.
Trade-offs: The response depends on how advanced the underlying condition is and whether the vascular changes in the lungs have become self-sustaining. Some underlying processes, such as advanced fibrotic lung disease, may not be reversible, and managing multiple conditions simultaneously can involve several medications with overlapping side effects.
Oxygen supplementation
Providing supplemental oxygen, either during acute episodes of respiratory distress or as a longer-term measure at home, can reduce the stimulus for pulmonary vessel constriction triggered by low oxygen levels. Oxygen can be delivered via a mask, nasal prongs, or an oxygen cage, and some owners arrange home oxygen concentrators for ongoing use.
Trade-offs: Equipment can be costly and requires space, and not all animals tolerate masks or prongs comfortably. Oxygen therapy addresses hypoxaemia but does not lower pulmonary vascular resistance directly unless low oxygen was the primary trigger for vessel constriction.
Activity modification and environmental adjustments
Adjusting the intensity and duration of exercise, avoiding heat stress, and managing body weight can reduce the heart's workload and lessen episodes of breathlessness. Some owners find that shorter, more frequent walks or indoor play sessions allow their dog or cat to remain active without triggering significant distress.
Trade-offs: The degree of restriction needed varies widely, and some animals may become frustrated or gain weight if activity is curtailed too much. Environmental changes alone do not address the vascular or cardiac abnormalities but can improve day-to-day comfort.
Common misconceptions
"Pulmonary hypertension is always a progressive condition that cannot be slowed or stabilised."
The trajectory depends largely on the underlying cause and how responsive it is to management. Some animals, particularly those in whom the condition is identified early and an underlying trigger such as mitral valve disease or chronic bronchitis is addressed, may remain stable for months or years. Others, especially when vascular remodelling is advanced or the primary cause is not modifiable, may show more gradual decline despite treatment.
"A dog or cat with pulmonary hypertension should not be allowed to exercise at all."
Complete restriction is rarely necessary and can lead to muscle loss, weight gain, and reduced quality of life. Most animals benefit from gentler, shorter activity sessions tailored to their tolerance, with attention to avoiding overheating or situations that provoke significant breathlessness. The appropriate level of activity varies between individuals and often needs adjusting as the condition changes.
"Coughing in a dog with pulmonary hypertension means the condition is getting worse."
Coughing can arise from several sources in animals with heart or lung disease, including airway inflammation, pressure on the airways from an enlarged heart chamber, or fluid accumulation. A change in cough character or frequency may signal a shift in the underlying process, but it does not always indicate progression of pulmonary hypertension itself. The pattern is often assessed alongside other signs such as breathing rate, exercise tolerance, and findings on examination or imaging.
Related conditions
Pleural Effusion
Pulmonary hypertension can contribute to pleural effusion when the increased pressure in the lung vessels and the strain on the right side of the heart lead to fluid leaking into the chest space. In some cases, pleural effusion may also be investigated as a possible cause of respiratory signs before pulmonary hypertension is identified.
Hypertrophic Cardiomyopathy in Cats
Hypertrophic cardiomyopathy in cats can lead to pulmonary hypertension when impaired filling of the heart causes pressure to build backwards into the vessels of the lungs. This connection means that cats with known heart muscle disease may be monitored for changes in breathing effort or exercise tolerance.
Dilated Cardiomyopathy in Dogs
Dilated cardiomyopathy in dogs can result in pulmonary hypertension when the weakened heart fails to move blood forward efficiently, causing pressure to rise in the pulmonary circulation. Dogs with this heart condition may show overlapping signs such as coughing, reduced stamina, and breathing changes.
Atrial Fibrillation
Atrial fibrillation can occur in dogs with pulmonary hypertension, particularly when the right side of the heart becomes enlarged and strained by the increased pressure in the lung vessels. The irregular rhythm may compound the circulatory challenges and influence how the condition is monitored over time.
Pericardial Effusion
Pericardial effusion can sometimes be considered during investigation of breathing difficulty and exercise intolerance, as it can produce overlapping signs with pulmonary hypertension. In some cases, fluid around the heart may also contribute to changes in circulation that affect pressure in the lung vessels.
Many animals with pulmonary hypertension live with other conditions affecting the heart, lungs, or clotting system, and exploring those areas can add useful context to what is being observed at home. The pages on mitral valve disease, chronic bronchitis, and thromboembolism describe patterns that sometimes overlap with or contribute to the picture. Conversations about monitoring strategies, medication adjustments, and what changes might warrant re-evaluation tend to evolve over time as the condition and the household's experience with it develop.
Last reviewed: 30 June 2026 · Dr Alastair Greenway MRCVS