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HCM Heart Disease in Cats

HCM heart disease in cats is a condition that causes the heart muscles to thicken. Further, it can affect kittens and adults alike, as well as any breed and gender. In addition, it’s estimated that anywhere from 15% to 30% of cats have HCM. However, most cats with HCM show no signs of disease. On top of that, we had to put Meow Meow to sleep recently due to complications related to HCM. As a result, it’s my sincere hope to prevent other pet parents from losing their cats in like manner.

Typical for me, when we or our pets go through an illness or injury, I scour the web for as much information as I possibly can to understand, and to hopefully prevent or find a solution to the issue. What started as a limp in Meow Meow rapidly progressed to lameness in only a matter of a couple of days. At prior vet visits, we were never told she had heart disease; never heard the words heart murmur, mitral valve dysplasia, or arrhythmia.

What caused Meow Meow’s lameness was feline aortic thromboembolism, otherwise known as FATE or saddle thrombus. And once cats are diagnosed with FATE, such as Meow Meow was, there is rarely good news. Therefore, even though saddle thrombus essentially brought about Meow Meow’s death, HCM heart disease was at the root of it.

What Causes HCM Heart Disease in Cats

bengal cat lying on the floor
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Genetic predisposition of HCM is the prevailing cause in many cat breeds, including Ragdoll, Sphinx, and Maine Coon. But HCM is also readily recognized in other purebred cats, including Bengal, Shorthair, Norwegian Forest, and Persian. So heredity is thought to be a determining factor with those breeds as well.

Although, other cat breeds, including mixed breeds, are speculated to have similar genetic causes to their HCM, work directed toward finding those remains unfruitful as of yet. Plus, mixed breed cats generally either don’t have well-documented family history or no family history of HCM. Thus, scientists believe there are also other, unknown causes of HCM.

Though, according to Cornell Feline Health Center, both hypertension and hyperthyroidism lead to HCM. Lastly, chronic kidney disease (CKD) and heart disease are often linked together in humans and cats; either one can provoke the other.

Symptoms of HCM in Cats

close up photo of dark gray British shorthair cat
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First of all, since cat owners don’t regularly exercise cats, unlike their dog counterparts, there might seem to be no symptoms of HCM heart disease in cats. Often dubbed the silent killer, because pet parents aren’t aware their fur baby has it until heart failure, FATE, or even sudden death.

But that doesn’t mean changes aren’t occurring. Even as the heart becomes less effective, your cat’s body makes up for the disease, concealing symptoms.  Think of small adjustments their body makes over time, ones we don’t register. Sadly, extended activation of such compensatory mechanisms damages the heart muscle and other organs in the end stages of the disease. Therefore, for clarity, I’ll divide the symptoms into 2 distinct medical conditions.

Congestive Heart Failure (CHF)

orange tabby cat wrapped in gray and white blanket
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CHF occurs if your cat’s heart isn’t pumping enough blood to other parts of their body, causing fluid to back up in the lungs.  Humans with CHF often compare it to drowning. And according to BMC Veterinary Research, cats affected with HCM have been shown to carry a 23.8% risk of developing congestive heart failure. Furthermore, symptoms of CHF in cats include:

  • Heart murmur
  • Abnormal heart rate or rhythm
  • Increased time spent sleeping while less time being active or playing
  • Weight loss, including decreased appetite and vomiting
  • Elevated breathing rate and/or effort
  • Pale or blue gums and cold extremities
  • Fainting or loss of consciousness
  • Open-mouth breathing or panting
  • Ungroomed appearance–upon close inspection, they might have dandruff in their fur, and/or long claws
  • And sudden death


black and white digital drawing of a cat showing thromboembolism, with heart, aorta and saddle
Digital Art, Courtesy of Sarah Smith

A thromboembolism is a blood clot that breaks off and causes a blockage.  And based on Purdue College of Veterinary Medicine, as of 2003, thromboembolism was observed in around 50% of cats with HCM. In addition, where the clot breaks off and settles determines the symptoms.

  • Stroke – a blood clot that blocks blood flow in the brain.  And signs consist of seizures, weakness, blindness, falling, muscle spasms, and coma.
  • Pulmonary embolism – a blockage that occurs in the lungs. And the signs are labored and rapid breathing. But the cat can also cough, have blue-tinged gums, faint, and/or go into shock. In addition, sudden death is also possible.
  • Aortic thromboembolism, aka saddle thrombus. 89% of cats with saddle thrombus have some form of heart disease. However, HCM is the one most often to blame. And saddle thrombus appears because a blood clot travels from the aorta and settles in the saddle, cutting off ALL circulation to one or both back legs. Additionally, it generates extreme pain and paralysis, and is often fatal.

Furthermore, in some cats, the strain of FATE deteriorates their cardiomyopathy leading to acute congestive heart failure.  So you see, a cat can have both saddle thrombus and CHF with cardiomyopathy. Though, it’s not common. And if it happens at all, it’s usually later in the disease.

How HCM Heart Disease in Cats is Diagnosed

2 vials of blood samples
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Unfortunately a DNA test is not how heart disease in cats is definitively diagnosed. Seeing that some cats that are predisposed to it don’t fall ill with HCM, even as other cats aren’t do. However, your pet’s veterinarian might hear a heart murmur at a routine office visit. Or another symptom might pop up, in which case the vet may recommend

  • proBNP blood test that measures the NT-proBNP hormone that’s released by stretched or stressed muscle cells in the heart. Despite being reported to have a 90% accuracy rate, there are other issues that can influence the test results.
  • echocardiogram is considered the gold standard when assessing the heart. This feline echo shows an image of the heart so veterinarians can then evaluate the heart size, shape, and the way it functions. Moreover, the veterinarian will be able to measure wall thickness, examine heart valves, and check blood flow. Echocardiograms can also be used to detect some heartworm infections.

Depending on your pet’s symptoms, your veterinarian may recommend a chest X-ray and/or an electrocardiogram (ECG) besides. The X-ray would look for fluid on the lungs. And the ECG would reveal any heart rhythm abnormalities.

Just be aware that if your cat doesn’t have HCM heart disease now doesn’t mean they won’t at some later time. Thus, if you have a high-risk breed, like one listed above, you should get them regularly tested.

Treatment for HCM in Cats

4 different pill bottles and 3 packets of medications next to blood pressure cough on wooden boards
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Fortunately, many medications formulated for people are also prescribed for cats with similar issues, as you’ll see below. However, don’t give any medicines to your pets until clearing it with your veterinarian first. Obviously dosages are completely different. In addition, disease progression will dictate treatment. But overall, the veterinarian may want to

  • slow your cat’s heart rate, correct arrhythmias, and lower blood pressure

Beta blockers like atenolol can slow heart rate and lower blood pressure. And calcium-channel blockers, such as Cardizem, are used for cardiac arrhythmias.

  • minimize clot formation

Plavix is usually better than aspirin at preventing further clots, according to Morris Animal Foundation. .

  • alleviate fluid build-up with CHF and change your cat’s diet

Diuretics like furosemide are used to drain excess fluid from the heart and/or lungs. Plus, oxygen therapy and needle aspiration are additional options if congestive heart failure is severe.

Also, your cat’s veterinarian likely won’t recommend changing any diet UNLESS your fur baby has congestive heart failure. That’s because unrestricted sodium intake for cats with CHF causes fluid retention. Talk to your veterinarian, or look here for ideas on what to feed your cat if they have CHF.

  • and lastly, give your cat pain medicine if needed

Prognosis of HCM Heart Disease in Cats

orange tabby cat lying on a green surface
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There are many variables involved when evaluating the prognosis for HCM in cats, like your cat’s age and how advanced the heart disease is. In addition, how well your cat responds to treatment affects the outlook as well. However, generally HCM heart disease is a progressive disease. Usually once symptoms appear, unless the first one is a blood clot, cats live about ~ 2 years. Otherwise, the odds are less than that.

Moreover, it’s vital to understand that heart medications don’t cure HCM. Although, they can prevent the disease from getting worse, and/or from causing secondary issues. Nevertheless, the best plan is to get cats diagnosed early, before any symptoms start.

HCM Heart Disease in Cats

close up of tortoiseshell cat sitting on a couch
Meow Meow Kitty Kitty

As I’ve learned about hypertrophic cardiomyopathy, and all of the resulting symptoms and complications, I realized why we didn’t notice the subtle signs in Meow Meow. She was a middle-aged cat when she came to live with us. Perhaps if she was kitten or a year old back then, things might have been different. But when Meow Meow came to us, she was already deep in her habits of sleeping all day. Therefore, we had nothing with which to compare her behavior.

Again, HCM is a degenerative disease, especially once symptoms start showing up. But it doesn’t have to be a death sentence. Even something as simple as excessive sleeping or an unkempt appearance should be taken as a sign that something is off. Because the sooner treatment can be started, the better your cat’s fighting chances are.

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