It is not something any owner wants to hear: “Your dog has a heart murmur.” But the truth is, having a heart murmur is very different from having heart disease or heart failure. This article explains what a heart murmur is and what the implications of having a murmur are, both good and bad. Read on to learn more about heart murmur in dogs.

Murmur Definition: What is a Heart Murmur in Dogs?

The term ‘murmur’ refers to turbulent blood flow within the heart that creates an extra noise or heart sound. It’s this noise that the vet hears when listening with a stethoscope against the dog’s chest.  This is described as a ‘heart murmur’.

The noise comes about because the heart is designed like a one-way street. Blood is only meant to flow in one direction on its journey through this organ. Much like putting a bolder in a river, if something interrupts the blood flow, the turbulence creates a noise. These extra heart sounds are known as a murmur.

Anatomy of the Dog Heart: What’s Causing the Irregular Heart Sounds!

The anatomy of the heart is quite miraculous. The precision with which all the working pieces fit together is a marvel. But this means when a part becomes faulty, such as a thickened heart valve, just like a misfiring car engine it no longer works so effectively.

One of the most common causes of heart murmur in dogs is valve disease. For example, oxygenated blood from the lungs enters the left atrium. The atrium contracts pushing the blood into a larger chamber, the left ventricle. The latter then contracts to push blood around the body.

A valve (the mitral valve) is like a one-way swing door, policing the path from the left atrium to the ventricle. A common problem in older dogs is a myxomatous mitral valve. This is just a fancy way of saying the valve becomes stiff and thickened. When the valve affected is the mitral valve, the condition is known as mitral valve disease.

In practical terms, the valve no longer shuts snuggly, like a door with a chunk taken out of it. The upshot is blood can flow, in the wrong direction, which the vet hears as a murmur.

Heart valves are tethered to the heart muscle with special stretchy cords called ‘chordae tendineae’. Again, these can stretch and allow leakage. More serious still is if those chords rupture.

Can It Lead to a Dog Heart Attack?

This can cause a seemingly normal dog to develop acute heart failure in a form of doggy heart attack.

But it isn’t just leaky valves that can cause a murmur. Thickening of the heart muscle (hypertrophic cardiomyopathy) or an enlarged heart (dilated cardiomyopathy) can also do this.

What About Heart Murmur in Cats?

Yes, a heart murmur in cats can happen, just as other pets can. But our feline friends do less ball chasing than their canine cousins, and tend to take life easy. This means cats are particularly good at hiding the early symptoms of heart disease.

This makes regular vet checks even more important for cats. A veterinarian picking up the murmur early is best placed to prevent heart disease developing.

Some dog breeds carry a higher risk of developing heart disease than others. This is because of a genetic link that is passed down from the parent to the puppies.

If the puppy is born with a heart defect this is known as a congenital or ‘present at birth’ problem. Examples of this include a patent ductus arteriosus or subvalvular aortic stenosis.

However, it’s also possible for the heart to normal at birth and start to fail prematurely in adult life. The latter is known as acquired genetic heart disease.

But life is rarely that simple and a heart murmur in dogs are no different. No all acquired murmurs or congenital heart disease are inherited, but can come about for other reasons.

What is clear is that certain breeds, such as the Cavalier King Charles Spaniel, have a vastly higher risk of developing a murmur than others.

In an ideal world, breeders would only use dogs with healthy hearts to breed from. But again, life is rarely straightforward.  An adult may have a normal heart and only develop the heart murmur in dogs in later life, when their breeding career is over.

Types of Dog Heart Murmurs

The most common type of murmur is a systolic murmur. This refers to the murmur occurring as the heart contracts. A less common murmur is a diastolic murmur, which occurs as the heart relaxes.

The good news is that some murmurs are described as ‘innocent murmurs’. This term means that although there is turbulent blood flow, the heart is coping just fine.

Think of this as a small rock in the middle of a river. The rock causes a little turbulence locally, but doesn’t affect how the river runs. In contrast, imagine a huge boulder dropped into the same river. This seriously diverts the flow of water so that it overflows the banks.

Such is the difference between a murmur causing a heart disease and innocent heart murmur in dogs. Some of the murmurs heard in young puppies or giant breed puppies can be innocent murmurs, which the dog grows out of.

Sadly, this isn’t always the case, and so a veterinary cardiologist may need to scan the heart to tell the difference.

Signs Your Dog has a Heart Problem!

A heart murmur in dogs can lead normal lives for years. However, there may come a point when the heart starts to struggle. At this point, the dog may show signs of heart disease. Typically, this is when the dog starts to enter congestive heart failure.

Signs of this include:

  • Lack of energy
  • Reluctance to walk
  • Heavy breathing
  • Breathing more rapidly
  • A cough, especially at night or when resting
  • A blue tinge to normally pink gums
  • A racing heart rate
  • Fainting
  • Poor appetite
  • A swollen belly (right-sided heart failure.)

If you notice any of these signs, especially if the dog has a heart murmur, see the vet immediately.

Diagnosing Murmurs in Dogs!

The first step in diagnosing the murmur is to recognize its presence. This is done by the vet or cardiologist listening to the heart with a stethoscope.

They will listen over all of the chest areas, on both the left and right sides. This gives clues as to the exact location within the heart from which the murmur is generated. This can help with reaching a diagnosis and deciding on a course of action.

If the murmur is grade III or above, then further tests may be necessary. Typically these include one or all of the following: an ultrasound heart scan, a chest x-ray, or an ECG.

These results give the vet an accurate view of the heart’s health and what treatment, if any, is necessary.

What is Murmur Grading? How Does it Work?

An important tool vets use to monitor a dog’s heart murmur is to ‘grade’ the murmur.

Grading is done on a sliding scale from 1 to 6.  This is where grade I is the softest of murmurs, which is difficult to hear with a stethoscope even in a quiet room. Grade 6 is the loudest murmur possible, where the turbulent blood flow is so marked it can sometimes be heard with the naked ear.

Treating Heart Murmurs in Dogs

Not all heart murmurs require treatment. Simply keeping the dog slim and active, is all that’s needed for grades 1 & 2.

With louder murmurs, there are medications which can support how the heart pumps and prolong a good quality of life. These drugs include angiotensin-converting enzyme inhibitors, diuretics, and positive inotropes.

A particularly important medication is pimobendan (TM Vetmedin.) This heart medication is unusual in that it’s been clinically proven to extend life when it’s started even before the dog becomes sick. However, it’s best started at a particular stage, where the heart is enlarged but the dog isn’t showing signs of congestive heart failure.

To hit this sweet spot involves dogs with quiet murmurs being scanned every 6 – 12 months. This allows the cardiologist to detect the heart enlargement early to start the dog on pimobendan.

Prognosis: Dog Heart Murmur Life Expectancy!

When a heart murmur is identified in your healthy dog, don’t panic. There’s every chance the dog may never develop full-blown heart disease.

Your vet will record the grade of the heart murmur in dogs as well as the heart murmur in cats, along with their heart rate. They will use this to monitor your canine companion and spot signs of deterioration. Should this happen, then further tests may be necessary.

Happily, modern medications can support a dog with heart disease and enable them to continue with the excellent quality of life for months or years to come.

Remember, each dog is an individual. Some defy the odds and outlive their predicted lifespan, whilst others can sadly suffer a catastrophic event, such as a heart attack, and deteriorate suddenly. But by being proactive and working with your vet, there’s every chance that you can make a difference and keep your pet happy for longer.

Common Question on Heart Murmur in Dogs

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Katelyn Son