Updated August 4, 2021
‘At A Glance’ (details below)
If A Pet Has A Heart Murmur
- Don’t panic! A heart murmur doesn’t mean much on its own.
- Learn the signs of heart failure so you know what to look for.
- Get your pet’s heart checked regularly
now dive deeper…
Max the Bengal cat has a heart murmur. He came in for something else and it was only during a routine physical that we found it. He’s not sick or showing any signs of heart problems. Should his owner worry?
Heart murmurs are common in dogs and cats. They can mean nothing but can also be essential to monitor.
What Is A Heart Murmur?
The audio clip above shows what to a vet would be a loud and obvious heart murmur. Instead of the normal lub-dub, lub-dub, the heart is going whoosh, whoosh. We call this type a systolic heart murmur, meaning it occurs only when the heart is contracting.
The whooshing noise is the sound of abnormal turbulence in blood flow. Normal hearts should produce a smooth laminar flow of blood so that the only noises you hear are the sounds of valves closing. “Lub” is the sound of the mitral and tricuspid valves, and “dub” is the aortic and pulmonary valves.
What Heart Murmurs Mean In Pets
The most likely reason why a pet has a heart murmur will be a heart defect. In puppies and kittens, there are also innocent murmurs. These are a murmur for which no cause can be found. The good news is that these can be up to half of the murmurs heard in young dogs and cats.
Do Dogs & Cats Grow Out Of Heart Murmurs?
Some puppies and kittens can grow out of heart murmurs by approximately 16 weeks of age. These murmurs are usually low grade and should show no signs of affecting the animal. Signs of a heart murmur being a problem are:
- Being quieter than their littermates
- More rapid respiration and heart rate
- Weak pulses and poor gum colour or refill
A vet can easily help you decide. Unfortunately, it’s more common for a murmur we hear in a young animal to be present for life. Even if mild, it is likely to be a congenital fault and so the animal should be desexed to prevent breeding.
Life Expectancy & Heart Murmurs
A dog or cat can live with a heart murmur for life. This is especially the case if a number of things are true:
- The murmur is only graded 1 or 2 (see the grading system below)
- The murmur does not progress or worsen
- There are no other signs of heart disease
In other words, you need a vet to keep an eye on it. While it’s always better to investigate a murmur, it’s acceptable to monitor it closely and investigate those of grades 3 and above in young dogs. In cats, it’s worth investigating all grades of heart murmur.
The prognosis for an older dog that develops a murmur depends on the speed at which it worsens. While it’s also OK to wait and see with mild murmurs, it’s best that you start getting more regular checkups.
Adult cats should start with blood testing to look for hyperthyroidism. Cats with heart diseases have more unpredictable lifespans than dogs. We see some cats that nearly die from severe failure able to live normal, symptom-free lives on treatment.
My Pet Has A Heart Murmur- What Do I Do?
Most heart murmurs in puppies and kittens are found by vets at the 6-week vaccination. This allows the breeders to make an informed decision and disclose the fault to potential purchasers. However, we still see a few that slip through, which is why we always advise a free checkup within days of arrival.
If your pet has a murmur, the best thing you can do is follow your vet’s instructions. Visit this page to read about the tests and treatment for heart disease that may be needed.
For cats, monitoring their resting respiratory rate provides useful early warning.
Grades Of Heart Murmurs
If your dog or cat has had a murmur diagnosed, you’ll want to know how bad it is and if it’s changing. In general, the higher the grade, the more likely a murmur is a concern*. Here’s how murmurs are graded :
- Heard only after several minutes in a quiet room with a quiet animal
- Easily heard but quieter than the heart sounds
- The same intensity as the heart sounds
- Louder than heart sounds but no ‘thrill’
- Loud with a thrill (vibration) now able to be felt
- Very loud with thrill and wide extent on the chest
Causes of Murmurs in Puppies
In order, the four most common causes of heart murmurs in shelter puppies are:
- Pulmonic Stenosis (PS): narrowing of the outlet from the right ventricle.
- Patent Ductus Arteriosus (PDA): failure of closure of a shunt at birth.
- Aortic Stenosis: narrowing of the outlet from the left ventricle.
- Ventricular Septal Defect: a ‘hole’ between the two chambers. Unlike the others, usually, the noisier these are, the smaller the hole.
About 1 in 400 shelter puppies have a murmur, though I would expect the rate to be higher for purebreds. The cause can only be properly diagnosed by cardiac ultrasound, although we often suspect a PDA just from the unusual ‘machinery’ murmur (audio clip above). Some, especially PS and PDA can even be cured or improved by surgery at a cardiac specialist.
Causes of Murmurs In Adult Dogs
There are only two common reasons in Adelaide for acquired murmurs in older dogs:
- Degenerative Mitral Valve Disease: a progressive leak in the valve between the left atrium and ventricle. This is the classic loud murmur of old small dogs that gradually worsens with age.
- Dilated Cardiomyopathy: thinning and ballooning of the heart muscle, especially common in large breed dogs. Sometimes the murmur can be quiet even when the problem is severe.
Both of these can be successfully managed if monitored closely and treated early.
Causes of Murmurs in Kittens
In order, the three most common causes of heart murmurs in shelter kittens are:
- Ventricular Septal Defect
- Aortic Stenosis
- Hypertrophic Cardiomyopathy: a heart disease where the muscle becomes enlarged and thickened
Around 1 in 300 kittens have a murmur. It’s likely that purebreds get other diseases as well such as valve defects and dilated cardiomyopathy.
Causes of Murmurs in Adult Cats
Acquired murmurs in older cats are almost always caused by heart muscle diseases called cardiomyopathies. We see three sorts:
- Hypertrophic: the most common, especially with thyroid problems or older male cats.
- Restrictive: an inflexible heart, probably with a similar cause to hypertrophic.
- Dilated: like the dog disease, especially in Maine Coons and Ragdolls.
Max, by the way, will be just fine.
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By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. These help topics are from a series regularly posted on email and Twitter. Subscribe via email here to never miss a story! The information provided here is not intended to be used as a substitute for going to the vet. If your pet is unwell, please seek veterinary attention.