Heart murmur

A heart murmur in dogs – that sounds worrying at first. It refers to an unusual sound that the vet hears with a stethoscope, somewhere between the normal heartbeats. It can arise whenever the blood flow in the heart or in the large vessels becomes turbulent instead of flowing evenly. Some heart murmurs are completely harmless, while others can be an early sign of a serious heart disease. They differ considerably in volume and timing within the cardiac cycle – and this usually tells the vet quite a lot about the possible cause.

What is a heart murmur?

If you have ever listened to a healthy heart, you know the typical “lub-dub” – two clear sounds produced by the opening and closing of the heart valves. However, as soon as blood flow through the heart becomes turbulent, an additional sound joins in. This can be a barely perceptible, quiet rustle or a distinctly turbulent sound that is noticeable even without much practice.

Types of heart murmurs

Vets classify heart murmurs according to three criteria: volume, timing in the cardiac cycle and duration.

1. Volume: Classification is on a scale from Grade 1 (barely audible) to Grade 6 (very loud, sometimes even palpable with the hand). A quiet sound is more difficult to detect and often – but not always – indicates less serious causes. A loud sound, on the other hand, often warrants a more thorough investigation.
2. Timing:
   • Systolic heart murmurs: They arise during heart contraction when blood is pumped from the ventricles into the large vessels.
   • Diastolic heart murmurs: They occur during the relaxation phase when blood flows into the heart ventricles.
   • Continuous heart murmurs: They are audible throughout the entire cardiac cycle and often indicate more serious findings.
3. Duration: Some sounds are short, while others last through the entire heartbeat cycle. Longer sounds generally indicate stronger turbulence in blood flow.

Causes of heart murmurs in dogs

The range of possible causes is wide – from harmless functional murmurs to treatable heart diseases.

Physiological (functional) heart murmurs:

• Such sounds occur quite frequently in puppies and young dogs, without any disease behind them. As a rule, they disappear once the heart has fully matured.
• They are usually quiet (Grade 1 or 2) and have no effect on the animal’s health.

Heart valve diseases:

• Mitral valve insufficiency: The mitral valve no longer closes tightly, allowing blood to flow back from the left ventricle into the left atrium. In older dogs – particularly small breeds – this is the most common cause of a heart murmur.
• Aortic and pulmonary valve stenosis: Narrowed aortic or pulmonary valves force the heart to build up more pressure to push blood through – and this creates typical sounds.

Congenital heart defects:

• Persistent ductus arteriosus (PDA): A vessel that should normally close after birth remains open. This leads to a characteristic continuous heart murmur.
• Atrial or ventricular septal defects: Holes in the walls separating the heart chambers allow blood to flow uncontrollably between the chambers – and this can be heard.

Cardiomyopathies:

• Dilated cardiomyopathy: Particularly known in large breeds. The heart muscle loses strength, which impairs blood flow and can generate sounds.
• Hypertrophic cardiomyopathy: Here, the heart muscle thickens, narrowing blood flow and also potentially leading to a heart murmur.

Anaemia (blood poverty):

• In severe anaemia, the heart pumps faster to compensate for the lack of oxygen in the blood. This accelerated, turbulent flow can trigger a functional heart murmur – which disappears again when the anaemia is treated.

Tumours or growths:

• Heart tumours or growths on the heart valves can mechanically disrupt normal blood flow and thus cause a sound.

Symptoms that may be associated with heart murmurs

Not every heart murmur becomes noticeable in the dog’s everyday life. With harmless forms, the dog remains completely free of symptoms. It looks different if a serious heart problem is behind it – then the following signs may appear:

1. Breathlessness or coughing: Both can indicate left-sided heart failure, in which fluid accumulates in the lungs and makes breathing difficult.
2. Reduced performance and tiredness: Affected dogs become exhausted more quickly, play less and appear generally slacker than usual.
3. Fainting spells (syncope): In aortic stenosis, for example, the heart may temporarily pump too little blood to the brain – with the result that the dog briefly collapses.
4. Belly water retention (ascites): Fluid in the abdominal cavity is a clear warning signal for right-sided heart failure, which can occur with certain heart murmurs.
5. Bluish discolouration of mucous membranes: A bluish discolouration of the mucous membranes (cyanosis) shows that the body is no longer being supplied with sufficient oxygen – a serious sign that requires immediate veterinary assistance.

Diagnosis of heart murmurs in dogs

It always starts with careful listening using the stethoscope. What follows depends on what the vet finds.

1. Auscultation (listening): The vet listens to exactly where the sound is loudest, how loud it is and when during the heartbeat it occurs. This alone already provides valuable initial clues.
2. Echocardiography (heart ultrasound): The most informative method. Heart valves, blood flow and muscle movement are visible in real time – a crucial basis for any further treatment decisions.
3. X-rays: X-ray images of the chest show whether the heart is enlarged and whether fluid has already accumulated in the lungs.
4. ECG (electrocardiogram): The ECG measures the electrical impulses of the heart and reveals heart rhythm disorders, which sometimes occur alongside heart murmurs.

Treatment of heart murmurs in dogs

Whether and how treatment is carried out depends on the cause and the severity of the underlying problem. Functional heart murmurs often require no therapy at all. For more serious findings, there are various approaches:

Drug therapy:

• ACE inhibitors: They lower blood pressure and relieve the heart – particularly used in cases of heart valve problems.
• Diuretics: Help to flush out excess fluid, which is particularly important in heart failure.
• Beta-blockers: Can slow down the heart rate and thus stabilise the heart.

Surgical procedures:

• In more severe cases, an intervention is necessary – such as a balloon valvuloplasty for pulmonary or aortic stenosis or the surgical closure of a ductus arteriosus. This sounds like a lot, but with timely diagnosis it is often associated with good prospects.

Lifestyle adjustments:

• Dogs with heart disease benefit from being protected against excessive physical exertion. Adapted nutrition and regular check-ups with the vet are part of the standard programme.

Prognosis

How things develop in the long term depends heavily on the cause. Functional heart murmurs often resolve on their own without ever affecting the dog’s life. Murmurs that indicate a serious heart disease usually require lifelong treatment and regular check-ups – but with the right therapy, many dogs retain a good quality of life, sometimes for many years.