What is congestive heart failure?

Congestive heart failure (CHF) occurs when severe heart disease causes pressure to build within the circulation, allowing fluid to leak into the lungs, the space around the lungs, or the abdomen. CHF does not mean that the heart has stopped; it means that the heart can no longer manage blood flow without fluid accumulating elsewhere in the body.

Heart disease and heart failure are not the same. Many dogs and cats have heart disease for months or years without developing CHF.

Common underlying diseases include degenerative mitral valve disease and dilated cardiomyopathy in dogs. In cats, the most common underlying heart disease is hypertrophic cardiomyopathy (HCM), although other forms of cardiomyopathy can also cause CHF. Congenital heart disease, heartworm disease and some pericardial disorders can also lead to CHF.

Where does the fluid collect?

• Left-sided CHF most commonly causes fluid within the lungs (pulmonary oedema). Fluid may also collect around the lungs (pleural effusion).
• Right-sided CHF most commonly causes fluid within the abdomen (ascites), although fluid may also collect around the lungs.

What signs might I see?

• A faster breathing rate while resting or asleep
• Increased effort to breathe, exaggerated chest or abdominal movement, or inability to lie comfortably
• Reduced exercise tolerance, weakness or tiring more easily
• Restlessness, especially at night, or sleeping in an upright position
• Coughing in some dogs; coughing is uncommon in cats with CHF and may have another cause
• Open-mouth breathing in cats
• A swollen abdomen, reduced appetite or discomfort from abdominal fluid
• Fainting, collapse, pale or blue-grey gums in severe cases

Important: Cats often hide signs until disease is advanced. Open-mouth breathing in a cat is never normal and requires immediate veterinary assessment.

How is CHF diagnosed?

Diagnosis combines your pet’s signs and examination findings with evidence of severe heart disease and abnormal fluid accumulation. Because other lung and airway diseases can cause similar signs, testing is important.

Investigations may include:

• Chest radiographs to assess heart size and look for fluid in or around the lungs
• Point-of-care chest ultrasound to rapidly identify fluid and support emergency decision-making
• Cardiac ultrasound (echocardiography) to identify the underlying heart disease
• Blood pressure, electrocardiogram and blood oxygen measurement
• Blood and urine tests to assess kidney function, electrolytes and other conditions that influence treatment
• NT-proBNP testing in selected patients, particularly cats in which respiratory stress makes imaging difficult

Unstable patients may need oxygen and initial treatment before all diagnostic tests can be performed safely.

Once your pet is stable enough to travel, referral for a comprehensive echocardiogram may be recommended. At QVS, some internal medicine clinicians can perform echocardiography; however, referral to a dedicated veterinary cardiology clinic may be advised for specialist assessment and ongoing management.

How is CHF treated in an emergency?

Emergency treatment aims to improve oxygen delivery, reduce distress and remove excess fluid while minimising stress.

• Oxygen therapy and calm, low-stress handling
• A loop diuretic such as furosemide to help the kidneys remove excess fluid
• Mild sedation when anxiety is worsening breathing difficulty
• Drainage of fluid from around the lungs or from the abdomen when it is restricting breathing or causing marked discomfort
• Additional medication to support heart function or control an abnormal heart rhythm when indicated

Pets with severe breathing difficulty may require intensive monitoring and, rarely, assisted ventilation.

Ongoing treatment at home

CHF is usually managed rather than cured. Treatment is tailored to the underlying disease and may change over time.

• Give every medication exactly as prescribed and do not stop or alter doses without veterinary advice.
• Expect increased thirst and urination while your pet is receiving a diuretic.
• Ensure constant access to fresh water unless specifically advised otherwise.
• Attend recommended rechecks and blood tests to monitor kidney function and electrolytes.
• Avoid very salty treats or supplements, but do not make major dietary changes without veterinary guidance.
• Contact your veterinarian if medication becomes difficult to give, your pet stops eating, vomits repeatedly or seems unusually weak.

Monitoring breathing at home

The sleeping respiratory rate is one of the most useful ways to monitor left-sided CHF at home. Measure it when your pet is deeply asleep, not panting, dreaming or recently active.

• Watch the chest rise and fall. One rise and fall equals one breath.
• Count breaths for 30 seconds and multiply by two, or count for a full minute.
• Record the result regularly so you learn your pet’s normal pattern.

Most dogs and cats with well-controlled CHF have a sleeping respiratory rate below 30 breaths per minute. A consistent rise above your pet’s usual rate is often more important than one isolated reading. Follow the individual threshold given by your veterinary team.

Seek urgent veterinary care if:

• Breathing is faster than the threshold provided by your veterinary team or continues to rise
• Your pet is breathing with increased effort, cannot settle or cannot lie down comfortably
• Your cat is open-mouth breathing
• The gums appear pale, blue-grey or purple
• Your pet faints, collapses, becomes profoundly weak or is difficult to rouse
• The abdomen enlarges rapidly or breathing becomes restricted

Do not give an extra dose of heart medication unless your veterinarian has provided a specific emergency plan.

A special risk in cats: arterial thromboembolism

Cats with some forms of heart disease can develop a blood clot that travels from the heart and blocks circulation, most often to the hind legs. This causes sudden severe pain, weakness or paralysis of one or both back legs, which may feel cold. This is an emergency.

What is the outlook?

The outlook varies widely and depends on the underlying heart disease, the severity of the first CHF episode, kidney function, treatment response and whether complications develop. Many pets regain a good quality of life after stabilisation, although CHF usually requires lifelong medication and can recur or progress. In dogs, prognosis depends strongly on the underlying disease. For dogs with congestive heart failure caused by degenerative mitral valve disease, published studies report median survival times of approximately 9-12 months with contemporary treatment.

Dogs with dilated cardiomyopathy often have a shorter median survival, commonly around four months, although individual outcomes vary widely. In cats, published studies report median survival times after a first CHF episode ranging broadly from approximately 3 to 18 months. These figures are population estimates only: some pets have a much shorter survival, while others remain well for considerably longer.

Regular rechecks, medication adjustments and home respiratory-rate monitoring help identify deterioration early and support the best possible quality of life.