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HCM testing in cats

Writer: Joel
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Updated on: April 20, 2021
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Humans and animals suffer from similar diseases, including obesity, heart disease, cancer, diabetes, and kidney diseases.

There's been an earlier debate among veterinarians on whether cats suffer heart diseases. However, like many animals, cats can suffer some forms of heart diseases. This situation occurs when the heart doesn't perform at the optimal level, or when it doesn't perform at all. Most of the heart diseases cases in cats are rare, but they exist.

One of the most common heart conditions suffered by cats is hypertrophic cardiomyopathy, also known as HCM. Hypertrophic cardiomyopathy affects about 10-15% of cats and it's one of the common diseases found in most cat breeds.

In this article, you'll learn:

  • What is hypertrophic cardiomyopathy (HCM).
  • What causes HCM in cats.
  • What are the signs of HCM?
  • How vets diagnose HCM?
  • How often you should test your cat for HCM.
  • What to do if your cat is diagnosed with HCM.

What is hypertrophic cardiomyopathy (HCM)

Hypertrophic cardiomyopathy is a genetic condition that occurs in cats. This condition causes the heart muscle to become abnormally thick and strong. In biological terms, the walls of the left ventricle of the heart become so thickened that the blood volume pumped abnormally reduces. 

HCM is a continuous and progressive condition. If not well managed, most cats usually develop an unwanted heart failure. This might occur when the heart muscle is scarred enough to affect the overall heart function.

What causes HCM in cats?

There's no known cause of HCM in cats. However, there've been a lot of theories on what could be the possible cause of the disease. Three main conditions that may predispose your cat to HCM:

  • Genetics.
  • Hypertension and Hyperthyroidism.
  • Nutrition.

There is no concrete evidence that shows that the above conditions cause HCM. But, research suggests a possibility of them being the causes.


Genetic predispositions have been noticed in some cat breeds. Research has identified two mutations in genes associated with HCM. Cat breeds such as the Maine Coon cat and the Ragdoll have been identified to possess this mutated gene.

This research goes on to identify that HCM is an autosomal dominant inherited trait. In humans, over 130 mutations in about 10 genes cause HCM. Although this number has not been confirmed in cats yet.

The mutated gene responsible for HCM is expressed differently; this means it can be severe in some cats, may be mild in some, and some cats may not have any signs of the disease but will produce affected kittens. However, from all the genetic studies done on HCM in cats, no genetic cause of the disease has been identified.

Although veterinarian geneticists are working extremely hard to know the gene that causes HCM in cats, the study of the genetic cause of HCM seems bothersome. This is because there are just a few veterinarian geneticists and cardiologists available. 

Also, the problem of variation of genes may pose a problem. For example, the gene responsible for HCM in Ragdolls may be different from the gene expressed in the Maine Coon cat. The genetic studies would demand a study of each cat breed individually.

Hypertension and Hyperthyroidism

There are other potential causes of hypertrophic cardiomyopathy in cats. Other diseases such as hyperthyroidism and high blood pressure can also cause HCM in cats. Although they are not the primary causes of the disease, some studies show that hypertrophic cardiomyopathy developed in most hyperthyroid cats. 

Hyperthyroidism causes the thickening of the left ventricle of the heart and this can lead to congestive heart failure. If your cat suffers from hyperthyroidism, it will be necessary for the vet to also diagnose and check the cat for the possibility of HCM; due to an increased risk of getting the disease.


Nutrition may also cause HCM, but there's no known evidence to suggest that. However, nutrient-gene interactions can provide an opportunity to study the severity of HCM in cats. Since obesity is one of the risk factors of HCM, the study of nutrition and how food is processed in the cat's body can provide a clue on how it affects the heart.

Most cats with HCM are usually overweight, have higher glucose concentration and develop more quickly in size when compared to healthy cats. This clue suggests that studying the early development of cats and what they eat may be key to determine the influence of nutrition in hypertrophic cardiomyopathy.

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What are the signs of hypertrophic cardiomyopathy in cats?

The signs seen in cats with HCM are usually noticeable. Some cats show no signs of illness, especially in the early stages of the disease.  In other more severe cases, the heart muscle becomes so stiff that an apparent congestive heart failure occurs.  

The obvious sign of HCM in this case includes

  •  Fatigue.
  •  Difficulty breathing(dyspnea)
  •  Rapid breathing (tachypnea)
  •  Low activity.
  •  Pale mucous membranes.
  •  Collapse episodes.
  •  Sudden death.

These signs show that your cat might be suffering from an apparent HCM. The case of fatigue is caused by poor blood transportation in the cat's body resulting in a period of oxygen depletion for the body cells. If oxygen is low or absent, cells won't function well and tend to reserve energy by making your cat weak.

The difficult and rapid breathing is caused by the accumulation of fluid around the lungs or inside the lungs themselves. This may cause your cat to labor for breath, or breathe heavily. 

Cats, unlike dogs, don't usually get exercised (walking and other forms of exercise). This makes it incredibly difficult to notice the breathing problems and inability to exercise, which is also a sign of HCM onset.

The pale mucus membranes are a result of poor blood circulation around the body, causing the membranes around the mouth to appear pale.

The collapse episodes are when you may require aggressive medical attention for the cat. It's one of the critical signs of potential heart failure which may lead to sudden death.

How do vets diagnose hypertrophic cardiomyopathy?

Veterinarian cardiologists diagnose hypertrophic cardiomyopathy using an echocardiogram (ECG).  

Echocardiography is the gold standard for detecting HCM in both cats and humans. It involves the ultrasound scanning of the heart to detect irregular rhythm.

However, before applying any diagnostic methods, your vet is likely to run some minor checks. These checks include:

  • Heart Murmur

Your vet is likely to check for a heart murmur using a stethoscope. A Heart murmur is an abnormal sound caused by the irregular blood flow in the heart. Not all heart murmur will signify that your cat is suffering from HCM. 

Some heart murmurs are innocent, physiologic, or result from heart diseases such as HCM. Your vet would notice this and will determine if your cat requires extra diagnosis.

HCM testing in cats 3
  •  Gallop Rhythm  

Gallop rhythm is an irregular heart sound heard when a part of the heart contracts, allowing blood to flow into the stiff left ventricle. In HCM, where the left ventricle is already stiff, the vet can hear a third and fourth heart beat when they place a telescope on the cat's chest area.

  • Irregular heart rate  

Your vet would check the rate of your cat's heart beat. Your cat's heart rate is likely to be too fast or too slow when HCM is involved. Sometimes, the heart can beat for several episodes without pumping any blood. Your vet would run lots of tests to determine whether these conditions are temporary, or as a result of an onset of HCM.

  • Irregular heart rhythms  

As the heart is controlled by electrical impulses, minor disturbances can cause a change in these impulses leading to irregular heart rhythms, also known as arrhythmias. Normally, cats have irregular heart rhythms when they are stressed, nervous, or scared. 

However, it is necessary to take your cat to your vet at least once a year. Since irregular heart rhythm can also be a sign of HCM, your vet can detect the disease early and take necessary precautions in its management.

There are other options used to detect HCM in cats. Since an echocardiogram is expensive and usually not readily available, your vet may consider these equally effective but cheaper methods. These methods include:

  • Radiography 

Radiography is used to monitor and evaluate the cat's heart shape and size. However, there's a limitation to this method. Results from ordinary radiography fail to differentiate between cats with cardiac disease from the ones without cardiac disease. This is because heart conditions like HCM do not involve the enlargement of the heart.

  • Thoracic Radiography 

Thoracic radiography has become one of the most common diagnostic methods used in detecting heart diseases in cats. This method is mostly used to detect cardiogenic pulmonary edema (accumulation of fluids in lungs, caused by heart diseases). It has a low sensitivity in detecting the enlargement of the heart. However, It has higher accuracy in detecting other parameters associated with heart diseases. 

Thoracic radiography also has high accuracy in differentiating between cardiac and non-cardiac disease, making it a reliable tool in diagnosing cats for HCM.

  • Gene test 

Since genetics can give a clue about the presence of HCM in cats, a genetic test can be regarded as one of the diagnostic tools to consider. The gene test evaluates the genetic profile of the cat and determines if any gene mutation has occurred, which may predispose the cat to HCM.

The Maine Coon cats and Ragdoll are the few breeds of cats that may be predisposed to HCM genetically. They should be screened for HCM using the gene test. 

If you keep a Ragdoll or the Maine Coon cat, it's necessary to check them for any sign of hypertrophic cardiomyopathy. A simple genetic test requires you to do a simple cheek swab and send the sample to a genetic lab for genetic analysis.

HCM testing in cats 4

Other methods such as blood tests can also be considered as a diagnostic tool. Testing your cat for hyperthyroidism which is a risk factor for HCM should also be a priority.

How often should you test your cat for HCM? 

Usually, only cats with known signs of hypertrophic cardiomyopathy are tested for the disease. However, you should not rule out regular visits to your vet to be safe.

Echocardiography(ECG) is one of the best methods for diagnosing HCM. However, it's not a perfect method. Some cats go through ECG but the vets fail to detect any signs of HCM. The reason may be due to irregular veterinary visits; most cat owners only visit the vet when they notice abnormal behavior in their cats.

The best way to make use of this diagnostic tool is to visit your vet at least once a year. Regular visits will help the vet look at other details that may be associated with the disease. 

You can remind your vet to include the HCM test and diagnosis as part of the schedule during your visits.

Does HCM affect cats of all ages?

Yes. Hypertrophic cardiomyopathy affects cats of all ages. HCM has been detected in newborn kittens and adult cats. In humans, men are more prone to HCM than women. This situation is also the same with cats. 

In Maine Coons, the disease usually starts early at two to three years of age in males, and three to four in females. Although it rarely occurs in female cats as compared to the male. 

Ragdolls, in contrast, tend to develop HCM under one year of age. The testing guideline for other cats is not yet available. However, it seems reasonable to start testing your cat around 1 to 2 years of age.

Since HCM affects cats of all ages, you should not relax after one test. You may be required to test your cat yearly to avoid escaping any sign of HCM in your cat.

What to do if your cat is diagnosed with HCM?

It's not the end of the world if your cat gets diagnosed with HCM. Most cats live through the disease, but it requires a dedicated effort from the owner. 

When you get the results from the diagnosis, The first thing is to ask your vet how you will go about it. 

What lifestyle recommendations and precautions you may need.

Your vet is likely to provide adequate information you need to manage the disease and give your cat a better life. 

The next thing is to stick to the information given to you religiously and apply every step given. You can also pay regular visits to the vet; in case there is any other information or changes you need to make. 

If you're a breeder, you might need to do the following;

  • Remove all diagnosed cats from any breeding program. Don't breed any cat from the HCM-diagnosed cats. If this happens accidentally, monitor the kittens and test them for any potential occurrence of HCM.
  • Test and monitor all cats from the Maine Coons and Ragdoll breeds and make sure they are free from HCM before breeding.
  • Some cats can have one normal gene and one abnormal gene. These cats would pass 50% of the genes to the kittens. The best practice is to remove them from the breeding program entirely.

Applying these principles will have your cat live longer and healthier even with HCM. It can also help cat breeders to take extra caution while running a breeding program. 

Most HCM are mild. Some come with just heart murmurs. However, the condition can go from mild to severe if the cat owner doesn't show enough care to improve the cat's quality of life. 

Final words.

Cats suffer HCM as much as humans do. HCM stiffens the heart muscle, preventing the heart from pumping enough blood required for the overall well-being of your cat. If this is not well managed, it can lead to heart failure.

HCM occurs mainly in the Maine Coon cats and the Ragdolls. They are the only breed confirmed to have a genetic predisposition to the disease. Other cat breeds are yet to be studied.

There's no known treatment or cure for HCM for now. However, it is necessary to run several tests on your cat to determine whether it is prone to HCM or not. The best way to know this is to visit the vet regularly. 

Regular visits to the vet not only provide you with information about HCM, it may also uncover other underlying illnesses in your cat.

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