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Heart murmurs in dogs – what does it mean?

Heart murmurs in dogs can be picked up on physical examination by a veterinarian. Heart murmurs have different causes, with some being benign and others leading to heart failure. Read on to find out more.

What is a heart murmur?

Normally when listening to a heart with a stethoscope we hear the classical “lub dub” sounds of each heartbeat. A heart murmur is an abnormal sound that we can hear in addition to or instead of the normal heart sounds. Heart murmurs are graded on how loud they are on a scale of 1 to 6, with 6 being the most severe. Most murmurs that cause serious problems are at least a grade 3.

What is the significance of heart murmurs in dogs?

The significance of the murmur depends on the cause. Some murmurs are insignificant or non-pathological, meaning that they are not related to any underlying heart disease. Other murmurs are associated with heart disease and signify the need for treatment. The significance of the murmur will also vary depending on the intensity or grading of the murmur detected. It is important to remember that some heart diseases will not cause a murmur.

What are the most common causes of heart murmurs?

  • Murmurs due to valve disease

    There are four valves in the heart which help to maintain blood flowing in one direction. If a valve is too narrow, because it did not develop properly, this can lead to a heart murmur. These are more likely to be diagnosed in young animals and the defect is usually Aortic or Pulmonic stenosis. Valves can also become faulty with age leading to a regurgitation murmur. This means that a jet of blood flows back the wrong way, this is commonly seen in Mitral Valve Disease. Mitral valve disease is the most common cause of heart murmurs in dogs. For more information click here.

  • Murmurs due to a “hole in the heart”

    Sometimes during development the separate parts of the heart or major blood vessels do not seal off properly, leaving a hole. This hole affects the way the blood flows and can lead to a murmur. Common causes of these murmurs are Ventricular Septal Defects or Patent Ductus Arteriosus.

  • Murmurs in puppies

    Puppies less than 6 months of age with a heart murmur may have a congenital defect or an innocent (benign) murmur. These innocent murmurs occur due to fast blood flow through a small heart and will gradually disappear as the heart matures, usually by 6 months of age. It is virtually impossible to tell on clinical examination which of these murmurs a puppy has. To find out the cause referral to a veterinary cardiologist for further imaging is required.

  • Murmurs seen with other illnesses

    Murmurs can develop due to changes of the blood itself rather than the heart. For instance anaemia (low red blood cell levels) will cause the blood to be thinner and can lead to a murmur. Similarly low protein levels in the blood can cause a heart murmur.

Ultrasound dog

How do we diagnose the cause of a heart murmur?

The best way to diagnose the cause of heart murmurs in dogs is to perform a heart scan, also known as echocardiography. Some cases may require additional tests such as an ECG, blood tests or radiographs. Here at Rochford Vets we can perform basic heart scans but in some cases it is best to be referred to a specialist veterinary cardiologist.

During a heart scan the heart is assessed for its size and shape, as well as its ability to pump blood. Heart scans are non-invasive ultrasound scans which are often performed without sedation and by clipping a patch of fur on both sides of the chest.

How are heart murmurs in dogs treated?

Heart murmurs are an abnormal heart sound and not a disease in itself. So treatment of heart murmurs depends on the underlying cause of the murmur. Innocent murmurs require no treatment. Different heart conditions require individual treatment. This may involve lifelong medication to help the heart function better and to reduce the build-up of fluid in the lungs. Some congenital defects can be corrected by surgery at a specialist centre.

What is the prognosis for dogs with a heart murmur?

The prognosis of dogs witha heart murmur also depends on the underlying cause. Whilst heart murmurs are serious, most of the underlying causes can be treated or managed with medication. Dogs which have mitral valve disease have a better prognosis if started on treatment before heart failure occurs. Dogs that respond well to treatment have a fair prognosis and generally good quality of life. Depending on the cause and severity of disease some dogs may stabilise for a few months whilst others may be stable for a few years. The quicker that heart murmurs in dogs are diagnosed the more likelihood there is of a favourable outcome. This is one reason why annual health checks at the time of vaccination are invaluable.

If you have any concerns about your dog please call us on 01702 545558 to book an appointment with one of our vets.