CONDITION
Congestive Heart Failure in Dogs
Congestive heart failure describes what happens when the heart can no longer move blood efficiently enough to meet the body's needs, and fluid begins to accumulate in the lungs, chest cavity or abdomen as a result. It is not a disease in itself, but rather the end point of various heart conditions, such as valve disease, muscle disorders or rhythm disturbances, that have progressed to the stage where circulation becomes compromised. Many owners first notice a persistent cough, faster breathing at rest, or reduced stamina on walks. Some dogs become quieter, tire more easily, or seem reluctant to lie down flat. These signs tend to build gradually, though in some dogs fluid can build in the lungs over a matter of hours, producing laboured breathing at rest that cannot be relieved at home. A first episode of this kind is sometimes how previously unrecognised heart disease comes to light. The pattern often reflects which side of the heart is most affected, and how long the underlying condition has been developing. This page explores the signs that may be observed, the mechanisms that lead to fluid build-up, the tests used to assess heart function and guide decisions, and the range of approaches, medical and supportive, that exist to manage the condition over time. It does not tell you what your dog has, but it may help you understand what you are seeing and what questions may be worth exploring.
Why this matters now
Congestive heart failure in dogs typically develops as the end-stage manifestation of progressive cardiac disease. Myxomatous mitral valve disease (MMVD) is the most common underlying cause in small to medium breeds, while dilated cardiomyopathy (DCM) predominates in large and giant breeds. The transition from compensated heart disease, where the heart maintains adequate output through compensatory mechanisms, to decompensated heart failure may occur gradually or may be precipitated by factors such as arrhythmia development, dietary indiscretion, concurrent illness, or anaesthetic events. Most dogs that develop CHF are middle-aged to elderly, though breed-specific cardiomyopathies can produce heart failure in younger animals.
Heart failure follows a trajectory of progressive decompensation, though the rate varies considerably between individuals. Initially, neurohormonal compensatory mechanisms, such as activation of the renin-angiotensin-aldosterone system, sympathetic nervous system upregulation, and cardiac remodelling, maintain cardiac output at the expense of increased blood volume and cardiac workload. As these mechanisms become insufficient, fluid begins to accumulate. Left-sided failure produces pulmonary oedema (fluid in the lungs), while right-sided failure produces ascites (abdominal fluid), pleural effusion and, less commonly in dogs, peripheral oedema. Many dogs develop biventricular failure over time. The condition is managed rather than cured, with the goal of controlling fluid accumulation, reducing cardiac workload, and maintaining quality of life for as long as possible. Alongside this slow background course, decompensation can be abrupt. Fluid can accumulate in the lungs over hours rather than days, and the picture can move from a raised sleeping breathing rate to effortful breathing at rest, reluctance to lie down and pale, grey or bluish gums within the same day. Fluid at this level impairs oxygen uptake and is fatal without treatment, which in hospital typically involves injectable diuretics repeated over the first hours and oxygen supplementation. Many dogs treated at this stage stabilise and return to management at home, whereas the same episode left untreated can progress to respiratory failure.
Signals & patterns
Early signals
Coughing, particularly at night or when lying down
As pulmonary oedema develops or the enlarged heart compresses the left mainstem bronchus, a cough may emerge that is most noticeable during rest or recumbency. The cough may initially be soft and infrequent, easily dismissed as a throat-clearing sound, but tends to become more persistent as fluid accumulation increases.
Increased respiratory rate at rest
The resting respiratory rate (breaths per minute when the dog is calmly resting or sleeping) is a sensitive indicator of early fluid accumulation in the lungs. Normal dogs typically breathe fewer than 30 times per minute at rest. A rate above this threshold on a recount while the dog is settled, or a clear rise from the dog's own baseline, may indicate developing pulmonary congestion. In some dogs the rise develops over days, but in others it develops over hours, and a rate that keeps climbing while the dog is asleep usually reflects fluid that does not clear without treatment.
Reduced exercise tolerance
Dogs may begin tiring more quickly on walks, lagging behind on familiar routes, or showing reluctance to engage in activities they previously enjoyed. This reduced stamina reflects the heart's inability to increase its output sufficiently to meet the elevated oxygen demands of physical exertion.
Restlessness at night
Difficulty settling at night, frequent position changes, and apparent inability to find a comfortable sleeping position may reflect early respiratory discomfort. Some dogs prefer to sleep with their head elevated or in sternal recumbency rather than their usual position, as lying flat can make breathing harder when the lungs are congested.
Later signals
Laboured breathing and abdominal effort
As pulmonary oedema becomes more significant, breathing requires increased effort. The dog may show visible abdominal movement with each breath, flaring of the nostrils, or extension of the neck to straighten the airway. Breathing may appear fast, shallow, and effortful even at rest, and the dog may refuse to lie down. Fluid at this level impairs oxygen uptake, does not resolve on its own, and can progress to respiratory failure within hours.
Abdominal distension
Right-sided heart failure produces ascites: the accumulation of free fluid in the abdominal cavity. The abdomen may gradually enlarge, developing a pot-bellied appearance that contrasts with muscle wasting over the spine and hindquarters. The fluid may be detectable as a fluid wave on palpation.
Syncope or collapse
Fainting episodes may occur during exertion, excitement, or coughing fits as the failing heart cannot maintain cerebral perfusion during moments of increased cardiovascular demand. Many episodes are brief with quick recovery, but recovery is not reassurance. Fainting can reflect abnormal heart rhythms, which in some dogs, particularly those with dilated cardiomyopathy, are associated with sudden death, and the cause of a collapse cannot be determined at home.
Pale, grey or bluish gums
In heart failure, pale, grey or bluish gums are a late sign. A grey or bluish discolouration of the gums and tongue (cyanosis) indicates severe hypoxaemia, where blood oxygen has fallen far enough that tissues are short of oxygen, and pale gums can reflect poor circulation when the output of the failing heart falls. By the time the gums turn grey or blue, fluid in the lungs is usually extensive, and a dog in this state depends on oxygen supplementation and diuretic treatment to survive the episode. Pale gums with weakness can mean the heart's output has fallen far enough to be life-threatening in its own right. Normal pink gums do not exclude significant fluid in the lungs.
Click to read about the biological mechanisms
How this is usually investigated
Investigation of suspected heart failure combines physical examination findings with imaging and biomarker assessment to confirm the diagnosis, identify the underlying cardiac disease, and stage the severity of failure.
Thoracic radiography
Echocardiography
Cardiac biomarkers
Electrocardiography
Blood pressure measurement
Options & trade-offs
Management of congestive heart failure centres on reducing fluid accumulation, decreasing cardiac workload, and supporting remaining cardiac function. Treatment is lifelong and typically involves multiple medications that work through complementary mechanisms.
Diuretic therapy
Furosemide (frusemide) is the main diuretic used in CHF management, promoting renal excretion of sodium and water to reduce circulating blood volume and relieve pulmonary congestion. Spironolactone may be added for its additional neurohormonal benefits and potassium-sparing diuretic effect. Torasemide represents an alternative loop diuretic with more consistent oral bioavailability.
Trade-offs: Diuretics control the clinical signs but carry risks of dehydration, electrolyte imbalances (particularly hypokalaemia with furosemide alone), and prerenal azotaemia if doses exceed the patient's needs. The dose often requires escalation over time as the disease progresses and the kidneys develop diuretic resistance. Regular monitoring of kidney values and electrolytes helps guide dosing.
ACE inhibitor therapy
Angiotensin-converting enzyme inhibitors, such as benazepril (authorised in the UK for dogs with heart failure) and enalapril (which has no current UK veterinary authorisation and is prescribed under the veterinary medicines cascade), counteract the overactivated renin-angiotensin-aldosterone system, reducing vasoconstriction, decreasing aldosterone-mediated fluid retention, and reducing cardiac workload. They are widely used in dogs with CHF, although the evidence for a survival benefit is weaker and more mixed than that for pimobendan.
Trade-offs: ACE inhibitors can cause hypotension, particularly when combined with diuretics, and may affect renal function. Regular monitoring of kidney values and blood pressure is important during treatment. Given the mixed evidence, the possible benefit for an individual dog is weighed against these risks, and doses are adjusted to the individual.
Positive inotropic therapy
Pimobendan is a calcium sensitiser and phosphodiesterase inhibitor that improves cardiac contractility while also providing vasodilatory effects (inodilator). It has become a standard component of CHF treatment, with evidence of improved survival time and quality of life. In certain conditions, it may be started before the onset of heart failure.
Trade-offs: Pimobendan is generally well-tolerated but may increase the risk of arrhythmias in some patients. The dual mechanism of action (improved contractility plus vasodilation) means its effects are weighed against the rest of the drug regimen to avoid excessive haemodynamic effects.
Dietary modification
Moderate sodium restriction may help reduce fluid retention, though severe sodium restriction is generally avoided as it can activate neurohormonal systems that worsen heart failure. Maintaining adequate caloric and protein intake is important to prevent cardiac cachexia. Omega-3 fatty acid supplementation may provide anti-inflammatory and anti-arrhythmic benefits.
Trade-offs: Dietary changes must balance sodium restriction against palatability and adequate nutrition. Dogs with heart failure often have reduced appetite, so overly restrictive diets may worsen nutritional status. Commercial cardiac diets are formulated to balance these considerations but may not suit all patients.
Monitoring and dose adjustment
Home monitoring of resting respiratory rate provides owners with a practical tool for detecting early decompensation. Counting breaths per minute when the dog is calmly resting or sleeping, and keeping a record to compare against the dog's own baseline, can identify fluid re-accumulation before clinical signs become severe, enabling earlier intervention.
Trade-offs: Effective home monitoring requires owner education and consistent technique. Respiratory rate can be influenced by factors other than heart failure, including pain, anxiety, temperature, and concurrent respiratory disease. The value of home monitoring lies in comparing each count with the dog's own baseline. A single high count taken while the dog is unsettled can mislead, but a count that stays raised once the dog is settled is a change in its own right rather than the start of a trend to follow over days.
Common misconceptions
"Heart failure means the heart has stopped working"
Heart failure does not mean the heart has stopped or is about to stop. Rather, it means the heart's pumping capacity has declined to the point where it can no longer meet the body's demands without compensatory mechanisms causing fluid accumulation. Many dogs with heart failure continue to maintain reasonable activity levels and quality of life with appropriate medical management for months to years.
"Dogs with heart failure should not exercise at all"
While strenuous exercise may be inappropriate for dogs in heart failure, moderate, gentle activity is generally beneficial and helps maintain muscle mass, joint function, and mental wellbeing. The appropriate level of activity depends on the individual dog's clinical status and on the limit set by the vet looking after it. It is judged from the dog's comfort and breathing on the day, rather than on the assumption that a dog will stop before overexerting itself.
"Heart failure only affects old dogs"
While heart failure is more common in older dogs due to the progressive nature of the most common underlying cardiac diseases, it can occur at any age. Congenital heart defects can produce heart failure in puppies or young adults, and certain breed-specific cardiomyopathies may cause heart failure in middle-aged dogs. The age at which heart failure develops depends on the specific cardiac disease and its rate of progression.
Related conditions
Mitral Valve Disease in Dogs
Mitral valve disease is one of the most common underlying causes of congestive heart failure in dogs, particularly in small and toy breeds. As the valve leak worsens over time, the heart may eventually reach the point where it can no longer compensate, leading to fluid accumulation in the lungs.
Pulmonary Hypertension
Pulmonary hypertension can develop as a consequence of long-standing left-sided heart failure, when backed-up pressure from the failing left heart affects the vessels in the lungs. In other cases, pulmonary hypertension from other causes, such as lungworm infection, may itself contribute to right-sided heart failure and fluid accumulation in the abdomen.
Pleural Effusion
Pleural effusion, fluid in the chest cavity around the lungs, is associated in dogs mainly with right-sided or biventricular congestive heart failure, whereas in cats it is a common feature of left-sided failure. Fluid around the lungs restricts their expansion and can cause laboured breathing in its own right. The pattern of fluid distribution often reflects which chambers are most compromised and how circulation is being affected.
Chronic Bronchitis in Dogs
Chronic bronchitis and congestive heart failure can both cause persistent coughing and laboured breathing, which means they are sometimes considered alongside one another when an older dog presents with respiratory signs. The distinction often requires imaging and other tests to identify whether the problem lies in the airways, the heart, or both.
Atrial Fibrillation
Atrial fibrillation may develop in dogs with advanced heart disease, particularly when the upper chambers become enlarged and stretched as a result of long-standing valve problems or muscle disease. The irregular rhythm can in turn reduce the heart's pumping efficiency and contribute to the progression of congestive signs.
Dilated Cardiomyopathy in Dogs
Dilated cardiomyopathy is a major cause of congestive heart failure in large and giant breeds such as the Dobermann, in which the heart muscle weakens and the chambers dilate. Affected dogs may also develop abnormal heart rhythms, and some die suddenly before heart failure is recognised.
Pericardial Effusion
Fluid in the sac around the heart restricts filling of the right side and can produce abdominal swelling, weakness and collapse that resemble right-sided congestive heart failure. The two are distinguished by ultrasound, and pressure on the heart from pericardial fluid can become life-threatening over a short period.
Tracheal Collapse in Dogs
Tracheal collapse causes a harsh, honking cough in small and toy breeds, the same dogs in which mitral valve disease is common, so the two often coexist. A cough alone does not distinguish airway disease from heart failure; the resting breathing rate and chest radiographs help separate them.
Angiostrongylus (Lungworm)
Lungworm is present in the UK, and the adult worms live in the heart and pulmonary arteries. Infection can cause coughing, breathing difficulty and exercise intolerance that resemble heart failure, can lead to pulmonary hypertension with strain on the right side of the heart, and can also cause bleeding problems.
Patent Ductus Arteriosus
Patent ductus arteriosus is a congenital heart defect that can lead to left-sided congestive heart failure in puppies and young dogs when the abnormal vessel remains open.
Understanding the principles of heart failure management can help owners participate meaningfully in their dog's care. Learning to count and track the resting respiratory rate provides a practical monitoring tool that can detect changes before they become clinically obvious. Recognising the signs of fluid re-accumulation, such as increased breathing rate, return of coughing, reduced energy, or reluctance to lie flat, allows change to be picked up earlier. A sleeping breathing rate above 30 breaths per minute on a recount while the dog is settled, or clearly above that dog's own baseline, is a home measure closely linked to impending decompensation. A raised sleeping rate is not a trend to be watched over days: in some dogs it progresses to laboured breathing at rest within hours, and how much fluid is present cannot be judged at home. Effortful breathing at rest, open-mouthed breathing in a resting dog, grey or bluish gums, or an inability to settle lying down suggest that fluid is already impairing breathing, and fluid at that level is fatal without treatment. Pale gums can mean the output of the failing heart has fallen, which can also be fatal without treatment. A collapse may reflect fluid on the lungs, but it may instead be a fainting episode caused by an abnormal heart rhythm, which in some dogs carries a risk of sudden death. The cause of a collapse cannot be determined at home, and a quick recovery does not show which it was. The progressive nature of the underlying heart disease means that treatment protocols typically require adjustment over time, and familiarity with the medications, their purposes, and their potential side effects supports informed decision-making as the management plan evolves.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS