Just like humans - or any mammal in fact - it’s important for dogs to have good heart health. When you take your dog to the vet for a check-up one of the key things they look out for is heart murmurs. But do you know what a dog with a heart murmur looks like? 

What is a heart murmur in dogs?  

When a vet or vet nurse listens to your dog’s heart through a stethoscope, they are measuring the heart rate (number of beats per minute) and also listening to the sounds of the blood moving through the heart’s chambers. A normal heartbeat makes a clear, regular ‘lub-dub’ sound but in some dogs, abnormal movement of the blood through the heart changes the normal sound of a heartbeat. The vet may hear whooshing or muffled sounds. These abnormal sounds are known collectively as heart murmurs, but there are many different types of heart murmur.

Heart murmurs are common in dogs and certain types won’t cause any problems for your dog. However, some heart murmurs can be a sign of disease, making it crucial that they’re spotted quickly.  

What causes a heart murmur?

The heart is made up of four chambers - the left atrium, left ventricle, right atrium, and right ventricle. Between each chamber there is a ‘door’ known as a valve. The valves flap open when blood passes through, then close to stop blood flowing back into the previous chamber. Sound is produced when blood flows through each valve and moves around the chambers. If there is a problem with the valves or chamber walls, this can cause an abnormal sound, known as a heart murmur.

What causes a heart murmur? There are many possible causes for the various different types of heart murmur, and veterinary cardiologists point out that just listening to a murmur is not enough to properly diagnose an underlying problem if there is one.

Some common causes are:

• • Young puppies (especially large and giant breeds) may have what is known as an ‘innocent’ murmur during growth spurts - this type of murmur has no physiological impact on the dog but may continue to be monitored by the vet.

• Some dogs may develop a heart murmur while they have an infection or heavy burden of parasites, that then goes away when the infection is cleared.

• Abnormal structure or shape of one or more heart valves, which can be present from birth (congenital heart defect) or develop with age (degenerative valve disease).

• Some other types of developmental heart disease such as DCM (dilated cardiomyopathy) can cause a change to the rhythm of a dog’s heart; murmurs caused by DCM may come and go over time.

Symptoms of heart murmurs in dogs

You may be wondering ‘how does a heart murmur affect a dog?‘ Well, it really depends on the cause. The signs you’re most likely to notice are those of heart disease in general, such as:

• Stunted growth in puppies.
• Coughing.
• Weakness, fainting (syncope) or collapsing.
• Intolerance to exercise and decreased stamina.
• Heavy breathing or ‘puffing’ while they rest.
• Weight loss with no decrease in appetite.
• Loss of muscle tone.
• A distended abdomen.
• Pale or blue gums - this is an emergency! - you should keep the dog calm and visit your vet immediately.

Do all murmurs sound the same?

No - and if the vet suspects an underlying problem, they may recommend X-rays and an ultrasound scan of the heart and surrounding structures (an echocardiogram or ‘echo’) to make a full diagnosis. 

Heart murmur grades in dogs 

Heart murmurs are graded on a scale of I-VI and further defined by their position in the heart and the cardiac cycle. 

• Grade 1 heart murmur in dogs - This is the least serious stage and requires a quiet room to hear the murmur through a stethoscope.
• Grade 2 heart murmur in dogs - This is a soft murmur that’s easily heard through a stethoscope.
• Grade 3 heart murmur in dogs - The murmur can be easily heard on one side of the chest.
• Grade 4 heart murmur in dogs - The murmur can be heard on both sides of the chest.
• Grade 5 heart murmur in dogs - The murmur is much louder and can be felt when a hand is placed on the chest. 
• Grade 6 heart murmur in dogs - This is the most severe stage of heart murmur and it can be felt through the chest wall and can be easily heard with a stethoscope away from the chest.

Heart murmur in dogs life expectancy

The life expectancy for dogs with heart murmurs can vary based on the underlying cause of the murmur and how severe it is. 

Dogs with innocent heart murmurs and those that receive surgery for structural heart problems can usually live a long and happy life. Many dogs with other types of murmur may be able to enjoy an improved quality of life with treatment and regular monitoring. 

For a clearer answer on your dog's life expectancy you should consult your vet. 

How do vets diagnose heart murmurs in dogs?

Vets detect heart murmurs using a stethoscope during a physical examination. Once heart murmurs are detected, underlying conditions are identified using:

• X-rays (radiographs) - These allow vets to see the size of the heart relative to the surrounding structures. An enlarged heart may indicate heart disease.
• Electrocardiograms (ECGs) - These detect irregular heartbeats, irregular rhythms and abnormal heart rates that may go alongside heart murmurs.
• Echocardiograms (echos) - These find the location of a heart murmur and in some cases can identify the speed and direction of blood flow through the heart valves.
• Blood tests - These can identify underlying diseases that could have caused the heart murmur, such as heartworm disease, anaemia and hypothyroidism. 

Treatments for heart murmur in dogs

The treatment for a heart murmur depends on identifying any underlying health condition. If your dog’s heart condition needs to be treated, vets may prescribe a combination of medication, a specialised diet and supplements. Your dog may also need regular physical examinations and scans to monitor their heart health.

What to avoid if your dog has a heart murmur

There are a few things you can do to avoid heart murmurs, such as:

• As with humans, being overweight contributes to heart disease in dogs and makes existing disease worse. Ensuring your dog’s weight stays within the healthy range, feeding a good quality diet and keeping an eye on how many high calorie treats your dog is given can all help.
• Avoid breeding from dogs that have close family members who were born with heart problems. 
• Practise good dental hygiene for better overall health and to prevent bacteria getting into the bloodstream and eventually reaching the heart.

FAQs

Can my dog have surgery with a heart murmur?

This ultimately depends on the underlying problem and your dog's condition. You should speak to your vet about your dog’s particular situation. If a dog with a heart murmur does need to have a general anaesthetic, the veterinary team will take extra precautions to keep your dog safe.

Are certain breeds of dogs more susceptible to congenital heart murmurs?

Unfortunately, any type of dog can be born with an abnormally structured heart, although certain breeds are more likely to be born with different types of heart defect.

What causes heart murmurs in older dogs?

• Some types of congenital heart conditions (especially those affecting the valves) may not become apparent until later in life, when a murmur may be heard for the first time.
• MMVD (myxomatous mitral valve disease) is one of the most common types of heart disease to develop later in life. Breeds that are more likely to develop degenerative valve disease include:

• Cavalier King Charles Spaniels
• Chihuahuas
• Poodles
• Shih Tzus
• Whippets
• Yorkshire Terriers

• DCM (dilated cardiomyopathy) can cause heart murmurs that change or come and go as the disease progresses and/or becomes controlled by medication
• Causes originating outside the heart leading to ‘functional’ heart murmurs that are usually low grade (I-II out of VI) and don’t cause any symptoms or problems for the dog. Functional heart murmurs can be caused by infections, blood loss, abnormally low levels of protein in the blood, pregnancy, obesity and emaciation. They usually disappear when the cause is resolved.

Can anxiety cause heart murmur in dogs? 

Transient (temporary) heart murmurs can sometimes be caused by anxiety or stress due to the blood pumping quickly, however these usually go away when the stress level reduces.

Is a heart murmur dangerous in dogs?

This ultimately depends on the underlying cause of the heart murmur. The earlier it’s identified, the more options you and your vet will have to treat the murmur and help your dog to a long and happy life. If you are unsure, you should consult your vet.

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