Heart failure in dogs: symptoms, tests and treatment

Overview

Heart disease can remain symptom-free for a long time because the heart initially adapts to an increased workload. Enlargement can initially help a ventricle pump more blood with each contraction. When venous and capillary pressure becomes too high, fluid can move out of blood vessels into tissues or body cavities. Failure causing fluid accumulation is called congestive heart failure.

In left-sided failure, raised pressure is transmitted to lung blood vessels and can cause pulmonary oedema. In dogs with right-sided failure, fluid most often accumulates in the abdominal cavity. In some dogs, the main problem is insufficient blood flow to tissues.

Causes

The most common cause of left-sided heart failure in dogs is myxomatous mitral valve disease, or MMVD. A leaking mitral valve allows some blood to flow back into the left atrium during contraction. In dilated cardiomyopathy, the heart muscle contracts less strongly than normal. A congenital blood shunt can overload the heart and lead to failure.

Sudden rupture of a chord supporting the mitral valve can rapidly raise left atrial pressure. Persistent mitral regurgitation can cause the kidneys to retain salt and water. Fluid overload increases if the heart can no longer adapt to the greater blood volume.

Tricuspid regurgitation can also cause right-sided failure by raising right atrial and venous pressure. A ventricle can thicken if a narrowed valve or another obstruction increases the pressure against which it must pump.

Risk factors

The risk of failure relates to heart disease severity rather than age alone. Mitral valve degeneration becomes more common with age, particularly in small dogs. It is estimated to affect around one in three dogs over ten years old. This estimate concerns valve disease, which may be symptom-free despite existing heart changes.

Cavalier King Charles Spaniels are among the predisposed breeds. In large dogs, failure may be caused by dilated cardiomyopathy, found in breeds such as Dobermanns and Great Danes. Raised pulmonary arterial pressure can strain the right side of the heart.

In degenerative valve disease, the right-sided tricuspid valve is also affected in at least 30% of cases. Cavalier King Charles Spaniels may develop valve changes younger than many other breeds.

Typical symptoms

Faster breathing can be an early sign of pulmonary oedema, followed by laboured breathing as fluid increases. Failure can appear to start suddenly even when changes have developed gradually.

• Faster breathing than usual while asleep or resting quietly.
• Restless movement if breathing is difficult.
• Reduced ability to walk or play for as long as usual.
• Coughing in some dogs with pulmonary oedema.
• A rounded abdomen as fluid accumulates in the abdominal cavity.
• Weight loss with prolonged failure.

Fainting may relate to concurrent heart disease or arrhythmia; the episode itself does not establish pulmonary oedema. A dog struggling to breathe may extend the head and neck to get more air.

Complications and consequences

Large amounts of lung fluid hinder oxygen transfer from inhaled air into blood. Right-sided failure can enlarge the liver. Muscle mass may decrease even without a fall in scale weight. With severely impaired circulation, blood pressure may fall enough to cause cardiogenic shock.

Fluid around the lungs can restrict expansion and make breathing difficult. Neck veins can bulge with right-sided failure. Severely impaired circulation can make the paws and ears cool.

A registry follow-up included 445 dogs with stable heart failure from MMVD after treatment. Fluid-related symptoms returned within 180 days in 106 dogs. A larger left ventricle was associated with recurrence, but the measurement did not reliably predict it for an individual dog.

Right-sided failure can also cause swelling of the limbs or other peripheral areas.

Diagnosis at the vet

Is fluid accumulation caused by the heart?

The vet asks how breathing, energy and other symptoms have changed. A murmur in a coughing dog does not establish heart failure as the cause of the cough. Chronic bronchial disease is a common cause of long-term coughing in dogs. Chest X-rays check for changes consistent with fluid accumulation and assess heart size.

Pulmonary oedema can be hard to distinguish on X-rays when little fluid is present. Laboured breathing is stabilised before further investigations.

An anxious dog may breathe faster at the practice than when resting at home. In chronic left-sided failure, the left atrium is usually markedly enlarged. If pulmonary oedema follows sudden chordal rupture, it may not yet have had time to enlarge.

The underlying disease and severity

Echocardiography identifies the heart disease causing fluid accumulation. Cardiac ultrasound does not demonstrate fluid within lung tissue. An ECG helps identify arrhythmias accompanying heart failure. Blood tests assess kidney function and electrolyte balance, among other factors. Blood NT-proBNP can help assess whether respiratory symptoms are cardiac in origin.

Blood pressure is measured particularly when heart failure medication is planned. Urine specific gravity complements assessment of kidney function and fluid balance. Normal NT-proBNP makes heart failure a less likely explanation for coughing or breathlessness. Doppler ultrasound can also investigate findings suggestive of raised pulmonary arterial pressure.

In ACVIM stage C of MMVD, a dog currently has or has previously had signs of heart failure. Symptom control with treatment does not return the dog to an asymptomatic valve disease stage. Stage D means conventional treatment no longer adequately controls symptoms.

Treatment

Stabilising breathing

Supplemental oxygen is given during emergency care when needed. It helps raise blood oxygen when pulmonary oedema impairs oxygen transfer. A diuretic reduces lung fluid by increasing salt and water excretion in urine. Large amounts of abdominal fluid causing discomfort or affecting breathing can be drained at the practice.

An oxygen cage can deliver oxygen while minimising handling. In the most severe pulmonary oedema, mechanical ventilation may support breathing while medication takes effect.

A hospital follow-up included 100 dogs with pulmonary oedema caused by MMVD. Median age was 12.0 years. Median weight was 3.31 kg. Median hospital stay was 34 hours. Median oxygen therapy duration was 20 hours. Ninety-five of 100 dogs survived to discharge.

Median respiratory rate on admission was 64 breaths per minute. At discharge, 91 of 100 dogs no longer had clear signs of pulmonary oedema.

Follow-up information was obtained for 93 discharged dogs. Seventeen died or were euthanased because of heart disease within two months of discharge. Of the other 76, 22 were rehospitalised for pulmonary oedema within two months of discharge.

Ongoing treatment and monitoring

Long-term diuretic treatment aims to prevent fluid accumulation. Medication supporting heart muscle pumping may form part of long-term care. With atrial fibrillation, the vet may select treatment to slow an excessively fast ventricular rate. In valve-related failure, kidney values and electrolytes are checked 3–14 days after starting a diuretic. Some dogs may be considered for mitral valve repair at a specialist centre.

A vasodilator can ease blood flow by reducing vascular resistance. Potassium may be monitored during treatment because some diuretics can lower it. If fluid accumulation remains uncontrolled, the vet investigates factors such as kidney disease affecting drug response.

A randomised trial in dogs with valve-related failure measured time to cardiac death, euthanasia for heart failure or treatment failure. With pimobendan alongside other treatment, median time to this combined endpoint was 267 days. With benazepril alongside other treatment, it was 140 days.

Adequate energy intake helps prevent heart-failure-associated weight loss. The diet provides sufficient protein unless severe kidney disease requires a different approach. Assessment of salt intake also includes treats, table scraps and food used to give medicines.

If appetite decreases, the vet also considers whether medication could be affecting eating. Warming food can encourage eating when it is otherwise unappealing.

Prevention

Listening to the heart during a health check can reveal a murmur consistent with mitral regurgitation before failure develops. Annual auscultation is recommended as part of health checks for small breeds predisposed to MMVD. In asymptomatic stage B1, follow-up imaging may be spaced six to 12 months apart according to findings.

In asymptomatic stage B2 valve disease, the heart is already clearly enlarged. Treatment at this stage aims to delay heart failure. Dogs with hereditary heart disease should not be bred.

Mild asymptomatic stage B1 disease does not inevitably progress to heart failure. Breeding decisions also consider relatives' health information.

Important for dog owners

Count breaths when your dog sleeps quietly without panting. Count one chest rise and fall as one breath and continue for a minute. Sleeping respiratory rate is usually below 30 breaths per minute. Contact the treating vet if it repeatedly exceeds 30 or rises clearly above your dog's normal level.

Keep drinking water available once diuretic treatment has started. Record breathing effort and appetite changes as well as respiratory rate. Regular weighing helps detect changes whose cause can be investigated at follow-up. If breathing is difficult, take your dog to emergency care immediately and call ahead if possible.

Frequently asked questions

Does a heart murmur mean heart failure?

A murmur can be present during symptom-free valve disease. Murmur loudness does not generally directly indicate whether fluid has accumulated in the lungs. If a dog coughs, the vet also assesses possible respiratory disease such as chronic bronchitis, which is common in dogs.

Why is breathing best counted during sleep?

Heat or anxiety can cause panting and a faster respiratory rate. Measurements during quiet sleep in a cool room are easier to compare. Repeatedly increasing readings can warn of worsening heart disease.

Has heart failure gone away once breathing settles?

Treatment can settle breathing once fluid accumulation is controlled. A dog with valve disease still remains in the previously established heart failure stage even without visible symptoms. Home monitoring records sleeping respiratory rate to detect fluid returning as early as possible.

Why might a dog's abdomen enlarge?

Right-sided failure can cause abdominal fluid accumulation. A large volume can press on the diaphragm, leaving less room for lung expansion during breathing. With severe accumulation, a vet can drain fluid to improve comfort.

Why are kidney values monitored?

A dog with heart failure can also have kidney disease. After starting diuretics, creatinine and electrolytes can be compared with pretreatment values. Monitoring results help the vet plan ongoing care according to the dog's condition.