Hypertrophic Cardiomyopathy in Cats

Cardiomyopathy is the term used to describe any disease that affects the heart muscle. This is the most prevalent cause of heart failure in cats and the most frequent form of cardiac disease.

Cardiomyopathies (heart muscle diseases) are classified based on how they affect the structure and function of the cardiac (heart) muscle. The main classification is to split the condition into the following categories:

  1. Hypertrophic cardiomyopathy (HCM) is the most frequent kind of cardiac disease in cats, characterized by an increase in the heart’s muscle wall thickness. This lowers blood volume in the heart and hinders the heart muscle from adequately resting between contractions.
  2. Dilated cardiomyopathy (DCM) — This condition is when the heart’s muscular wall thins down, the heart enlarges, and the cardiac muscle cannot contract efficiently.
  3. Restrictive cardiomyopathy (RCM) —is characterized by fibrosis of the heart wall, which causes it to stiffen and become inelastic, preventing the heart chambers from filling correctly.
  4. Intermediate cardiomyopathy (ICM) — these patients have changes that indicate more than one type of illness, such as a mix of hypertrophy and dilatation.

Hypertrophic Cardiomyopathy (HCM)

In cats, hypertrophic cardiomyopathy is the most frequent heart illness. Feline Hypertrophic Cardiomyopathy (HCM) is a disorder in which the muscle walls of a cat’s heart enlarge, reducing the heart’s effectiveness and sometimes causing symptoms elsewhere in the body. Although the cause of HCM is unknown, the fact that it is more common in certain breeds (such as Maine Coons, Ragdolls, British Shorthairs, Sphynx, Chartreux, and Persian cats) and that mutations in several cardiac (heart) genes have been found in some cats with the disease suggests that genetics may play a role.

While the disease’s symptoms and prognosis (probable result) differ, appropriate diagnosis and treatment can reduce the likelihood of a cat with HCM experiencing specific symptoms and improve his or her quality of life.

The left ventricle (the heart’s primary “pump muscle”) of a cat with HCM thickens, resulting in a decrease in the capacity of the heart chamber and aberrant relaxation of the heart muscle. These alterations may cause the heart to beat faster, causing higher oxygen use and possibly oxygen deprivation in the heart muscle. Heart cells may die due to the lack of oxygen, causing heart function to deteriorate and arrhythmias to occur (in which the heart beats too rapidly, too slowly, or with an irregular rhythm).

In addition to these issues, inefficient blood pumping can cause a back-up of blood in the heart’s other chambers and lungs, leading to the development of congestive heart failure or the creation of blood clots in the heart.

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HCM is an inherited illness hypothesized to be caused by a genetic mutation in the genes that control heart muscle growth. One HCM mutation has been detected in the Maine Coon cat and the Rag Doll cat, but the genetic abnormality has yet to be seen in other purebred or domestic cats. More than one genetic mutation has been linked to the development of HCM in people, and the same is likely to be true in cats.

The following are some of the known underlying causes:

  • Cardiomyopathy as a result of other illnesses
    • Thyroid hyperthyroidism (overactive thyroid glands)
    • Hypertension (high blood pressure)
    • Acromegaly (excessive growth hormone production)
  • Nutritional problems
    • Taurine insufficiency is a condition in which the body lacks the amino acid taurine (causing dilated cardiomyopathy)
  • The cardiac muscle is infiltrative.
    • Lymphoma is cancer that damages the lymphatic system (a type of malignant tumor)
  • Toxic exposure is a concern for many people.
    • Some medications may have heart-related side effects.
  • Causes that run in families
    • Genetic abnormalities in Maine Coon cats and other breeds have been identified, leading to the development of cardiomyopathy.

What occurs when a person has cardiomyopathy?

Cardiomyopathy is a condition in which the underlying dysfunction of the heart muscle causes a reduction in heart function. However, the type of cardiomyopathy determines how the heart functions:

  • In HCM and RCM, the condition primarily affects the heart muscle’s capacity to relax appropriately between contractions. Diastole is the relaxation phase between cardiac contractions, and if it does not occur properly, the heart will not be able to fill with blood as efficiently. If the condition is severe, it can lead to heart failure and a condition known as “diastolic heart failure.”
  • Diabetes mellitus (DM) primarily impairs the ability of the heart muscle to contract (known as “systole”). This will impair the heart’s ability to pump (and expel) blood. In severe circumstances, this can also lead to heart failure, referred to as systolic heart failure.’

Heart Failure

If cardiomyopathy significantly impairs cardiac function, it can progress to heart failure (also known as congestive heart failure). Blood flow in the heart is compromised.

Clinical indications can appear in cats without warning, and some cats might decline exceptionally quickly. Some cats with heart disease display signs of collapsing, sometimes known as “fainting.” However, this is a rare occurrence frequently accompanied by significant disruptions in the heart’s normal rhythm.

Cats, unlike dogs, are rarely ‘exercised’ (e.g., taken for walks on a leash), making it harder to notice impaired exercise ability, which is often an early symptom of cardiac disease. Cats will most likely spend a little more time relaxing or sleeping, which may or may not be noticeable. Early disease detection (without a vet’s inspection) is typically tricky since cats are skilled at disguising signs of illness. Furthermore, until a ‘critical point’ is reached owing to illness progression or stress, there may be no evident indicators (which may result in the sudden or rapid development of quite marked signs).

The development of difficult breathing (dyspnoea) and more rapid breathing is the most typical symptom of heart failure in cats (tachypnoea).

Along with respiratory problems, cats may have cold extremities (e.g., ears and paws) and pale mucous membranes (gums and eyes), both of which indicate poor circulation. The mucous membranes of both eyes and mouth and the skin may occasionally display indications of cyanosis (a bluish color). Coughing is uncommon in cats who have heart disease, although it is common in dogs. Coughing in felines is more likely to be caused by an obstructive airway illness (such as bronchitis).

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Clinical Signs

Many cats with HCM appear to be healthy. Others may exhibit congestive heart failure symptoms such as difficult or fast breathing, open-mouthed breathing, and lethargy. When fluid accumulates in or around the lungs, these symptoms appear.

The production of blood clots in the heart is a significant and potentially life-threatening side effect of HCM. These clots could spread through the bloodstream and block blood flow in other parts of the body (thromboembolism). The result of a clot varies depending on where it forms, but in cats with HCM, clots frequently obstruct the blood supply to the hind limbs, producing acute hind limb discomfort or, in extreme cases, hind limb paralysis. Diagnosing HCM and effectively treating it can reduce the severity of clinical indications and the risk of thromboembolism.

Cats with HCM are in danger of abrupt death, even though it is a relatively uncommon condition.


Echocardiography, a method that employs sound waves to create an image of the heart, is used to detect HCM. These photos show the thicker walls and constricted volume of the heart’s left ventricle in cats with HCM. Other common illnesses, such as hyperthyroidism and high blood pressure, can produce comparable cardiac thickening. Before HCM can be diagnosed, these disorders must be checked out. Depending on echocardiographic findings and physical examination results, your veterinarian may order additional testing like chest radiography and electrocardiography.

New genetic testing may potentially assist in determining whether your cat is at risk for HCM. However, the findings of these screening tests should be carefully interpreted with the advice of a veterinary specialist, as not all cats with these mutations will acquire the disease.

What is the Treatment for Cardiomyopathy?

If an original cause of heart disease is discovered, treatment of this condition may result in heart disease improvement or reversal. Because the complete resolution of heart disease is possible if diagnosed and treated early, hyperthyroidism is the most treatable cause of cardiomyopathy. If there is no known cause for the heart illness, known as idiopathic cardiomyopathy, or if the heart disease persists after therapy for the underlying cause, medication may be required.

Treatment options vary depending on the circumstances, but they may include:

  1. If you have congestive heart failure, you should take diuretics to help lower the amount of fluid in your chest.
  2. Beta-blockers, which lower the heart rate if it is too high.
  3. Calcium channel blockers help the heart muscle relax, allowing for more efficient heart filling.
  4. Aspirin’s anti-thrombotic and anti-thromboembolic properties may be used to reduce the risk of thrombus formation and thromboembolic disease. Because aspirin can be hazardous to cats, it should only be used as directed by a veterinarian. Aspirin overdose can result in vomiting and internal bleeding if the amount or frequency of aspirin treatment is too high. If your cat exhibits these symptoms, stops eating, or appears sick, you should discontinue aspirin therapy and contact your veterinarian right away.
  5. Angiotensin-converting enzyme inhibitors (ACEIs) can also help in congestive heart failure.
  6. Blood pressure medications may be required to treat hypertension.

Unfortunately, the actual effectiveness of many medications in treating feline heart disease is uncertain, needing more clinical trials. Different drugs have different mechanisms of action; therefore, they may be helpful in other conditions. Diuretics are the most effective medications for treating the symptoms of congestive heart failure in general. Early detection and treatment of heart disease may reduce or delay its progression and maintain a good quality of life.


Cats with HCM have a mixed prognosis (probable result). Cats with modestly reduced heart function can routinely survive for years without showing any clinical indications.

Congestive cardiac failure, thromboembolism, and hypothermia are all symptoms that indicate a poor prognosis in HCM (low body temperature). Medical treatments, on the other hand, can often dramatically improve your cat’s quality of life.

Expected lifespan:

Most cats with HCM have a life expectancy of 6 to 18 months once they develop congestive heart failure. To discover more about your cat’s health and treatment choices, contact your veterinarian today.

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