Feline Hypertrophic Cardiomyopathy (HCM) in Cats: Causes, Signs, and Medication

Key Takeaways

Hypertrophic cardiomyopathy (HCM) is the abnormal thickening of the heart’s left ventricle.
Cats with HCM may not show symptoms until the disease has advanced, which can cause breathing difficulties, blood clots, and sudden death.
Early screening for HCM may improve quality of life and slow the progression of disease.
An echocardiogram is considered the gold standard to diagnose HCM in cats because it looks at the heart function in real time.

What Is Hypertrophic Cardiomyopathy (HCM) in Cats?

Like the human heart, the feline heart has four chambers—two smaller chambers on the top (the left and right atrium) and two larger chambers on the bottom (the left and right ventricle).

Hypertrophic cardiomyopathy (HCM) is the abnormal thickening of the heart’s left ventricle. As the wall thickens, the ventricle's inner space becomes smaller, making it less efficient at pumping oxygenated blood to the cat's body.

As a result, less oxygen-rich blood reaches the body, interfering with normal functioning. Because of this, the heart must beat faster to circulate blood, which further increases its need for oxygen. This leads to damage of the heart and worsening heart function.

Causes of Hypertrophic Cardiomyopathy (HCM) in Cats

HCM in cats can develop because of genetic factors (the most common cause) or underlying medical conditions that cause the left ventricle’s walls to thicken.

Genetics

One of the most common causes is an inherent disease of the heart muscle itself. Cat breeds commonly affected include:

Maine Coons

Persians

Ragdolls

Chartreux

Sphynx

Norwegian Forest

Bengals

Turkish Vans

American Shorthairs

British Shorthairs

These breeds are more likely to carry a mutation of a gene that normally supports healthy heart muscles. This mutation leads to abnormal thickening, death of heart muscle cells and scar tissue in the wall of the left ventricle, which prevents the heart from functioning properly.

Medical Conditions

In addition to genetics, there are several medical causes of HCM in cats.

Hormonal conditions: Both hyperthyroidism and acromegaly (excessive secretion of a growth hormone because of a tumor in the anterior pituitary gland near the brain) can stimulate growth of the muscular walls of the left ventricle.
Cancer: Cancer in the heart can increase the size and thickness of the walls of the left ventricle.
Kidney disease: Chronic kidney disease can cause high blood pressure, which puts additional strain on the left ventricle and can cause it to become thicker.

Symptoms of Hypertrophic Cardiomyopathy (HCM) in Cats

Signs of HCM in cats may include:

Loss of appetite
Heart murmur
Arrhythmias (abnormal heart rhythms)
Blood clots, which can cause pain/vocalization, trouble walking, cold rear limbs, vomiting, and trouble breathing
Heart failure, which results in fluid in the lungs, causing crackles, wheezes, and overall difficulty breathing
Fluid in the abdomen (ascites), causing visible abdominal swelling
Abnormal gum color—pale, gray, or blue gums
Blue foot pads and nailbeds
Weak or unstable pulse
Tiring easily during play/exercise
Lethargy/weakness
Fainting/collapse
Sudden death

How Do Veterinarians Diagnose Hypertrophic Cardiomyopathy (HCM) in Cats?

Diagnosing hypertrophic cardiomyopathy in cats usually involves a physical exam, blood tests, and heart imaging.

A veterinarian will start with a thorough physical exam, focusing on listening to the heart and lungs for any abnormal heart rhythms, murmurs, and any excessive crackling and wheezing during breathing.

They will also examine the cat’s feet and nail beds for signs of poor circulation, feeling carefully for any weak or unsteady pulses in the limbs, as well as look for any abnormal colors in the gums, such as blue, gray, or pale.

Following the physical exam, blood work, including a thyroid panel, will be performed to determine if there is a medical condition that might cause HCM.

A cat X-ray may be helpful in screening for HCM in advanced stages. Electrocardiograms (ECGs) can also be used to pick up any abnormal heart rhythms.

An echocardiogram (heart ultrasound) is the gold standard for diagnosing hypertrophic cardiomyopathy (HCM) in cats. An echocardiogram allows the veterinarian or veterinary cardiologist to evaluate heart muscle thickness, blood flow, and overall heart function as the heart is pumping in real time.

Importance of Early Screening for HCM in Cats

Early detection of HCM offers the best opportunity to intervene and potentially improve quality of life.

Because HCM develops slowly and typically doesn’t cause symptoms in the early stages, this disease can go unnoticed for a while. By the time symptoms have developed, cats have generally reached a more advanced stage of the disease and are at higher risk for complications, such as blood clots and difficulty breathing.

Early screening allows vets to prescribe medications to help manage symptoms when they are present. For cats who are not yet showing symptoms, vets may prescribe Felycin-CA1, the only medication indicated to prevent or delay progressive left ventricle hypertrophy.

Management of Hypertrophic Cardiomyopathy (HCM) in Cats

Your vet will focus on management of the disease rather than treatment of the disease itself since hypertrophic cardiomyopathy has no cure. Management for HCM in cats is aimed at addressing symptoms, slowing progression, and improving quality of life. The care plan depends on how severe the disease is and whether the cat has heart failure, abnormal heart rhythms, high blood pressure, or a risk of blood clots.

Medications for HCM in Cats

A variety of medications may help cats who have HCM, including:

A specific macrolide, such as Felycin-CA1, to prevent and delay progressive thickening of the left ventricle

Platelet inhibitors, such as clopidogrel, to prevent blood clots
Calcium channel blockers, such as diltiazem, to prevent fluid buildup and relax the heart
Beta blockers, such as atenolol, to slow heart rate, correct abnormal heart rhythms, improve heart valve function, and reduce blood pressure
ACE inhibitors, such as benazepril, to reduce blood pressure and fluid retention
Blood thinners, such as aspirin, to prevent blood clots. It’s important that pet parents never give over-the-counter medications to their cats without a veterinarian's approval.
Diuretics, such as furosemide, to reduce fluid buildup
Vasodilators, such as nitroglycerin ointment, to treat severe fluid buildup and improve blood flow

Breathing Assistance

Cats should have a respiratory rate of 30 breaths per minute (bpm) or less when they are sleeping. Pet parents can check this by counting how many breaths their cat has in six seconds and multiplying by 10.

If a cat is consistently above 30 bpm when resting, it is an early indicator of hypertrophic cardiomyopathy and the cat should be brought in for a veterinary checkup. This method can also be used to determine whether a cat with HCM is properly managed or if their condition is worsening.

Some cats may need routine thoracocentesis, a procedure that removes excess fluid from around the lungs, which can lower their sleeping respiratory rate and help reduce discomfort. Cats with severe, acute HCM and heart failure may need oxygen therapy in the hospital.

Stress Management

Stress can cause breathing difficulties and increase the risk of heart failure in cats with HCM. Anxious cats may be given sedatives such as butorphanol to keep them calm.

Supportive Care for Cats with Hypertrophic Cardiomyopathy (HCM)

Unfortunately, HCM in cats has no cure.

Cats with no symptoms may live a normal lifespan, but the disease is progressive and can worsen at any time. Speak with your vet about trying Felycin-CA1 to reduce the risk for severe symptoms.

Survival time is reduced for cats who have blood clots, congestive heart failure, and/or low body temperature. Once cats develop such symptoms, the average survival time could be less than one year.

There are a few things you can do at home to help support their quality of life.

Limit Stress

Stress can hinder breathing and increase the risk of heart failure in cats. It is important to set up a quiet space for your cat where they can rest away from any noise and activity of people and other pets.

Providing easy access to food, water, litter boxes, and soft perches near windows can support a stress-free environment.

Adjust Their Diet

Diet is another factor that can improve the quality of life for cats with HCM. Because HCM, especially with congestive heart failure, can cause loss of appetite, it is essential that cats be fed a high-quality, enticing food that is high in protein. This may require switching from wet food to dry food or vice versa.

Low-sodium broths or food toppers can encourage cats with lower appetites to eat more.

Provide Supplements

Cats on medications for congestive heart failure may lose too much vitamin B in their urine and require vitamin B supplements.

Omega-3 fatty acids, found in fish oils, can support muscle health.

Work closely with your veterinarian to determine what the best diet and supplements may be for your cat, based on their condition.

Prevention of Hypertrophic Cardiomyopathy (HCM) in Cats

Since HCM can be inherited or may be the result of other medical conditions, the disease is difficult to prevent.

Reputable breeders should test susceptible cat breeds for mutations in the A31P gene so that kittens produced from breeding stock do not inherit the mutation.

General care and proper nutrition for all cats can go a long way to supporting heart health and prolonging the asymptomatic stage of HCM. It is crucial for higher-risk cats (senior cats, cats with predisposed conditions, cats with the A31P gene) to be screened annually for any signs of heart disease.

If you are concerned about HCM in your cat, it’s best to speak with your veterinarian about their overall risk, which diagnostic tests are most appropriate, and how often those tests are needed.

Your veterinarian can also assist with developing a wellness and nutrition plan at home to ensure your cat has the best and longest possible life.  

HCM in Cats FAQs

What is the life expectancy of a cat with hypertrophic cardiomyopathy?

Cats with no symptoms may live a normal lifespan, but the disease can progressively worsen at any time. Survival time is significantly reduced for cats who develop blood clots, congestive heart failure, and/or low body temperature. Speak with your vet about trying Felycin-CA1 to reduce the risk for severe symptoms.

What are signs of HCM in cats?

Signs of HCM in cats include difficulty breathing, abdominal swelling, abnormal gum color, weak pulses, lethargy, and exercise intolerance. In severe cases, collapse or sudden death may occur. However, cats in the early stages of disease may not show any symptoms, which is why early screening is essential.

How fast does HCM progress in cats?

The progression of HCM in cats is highly variable. Some cats may go for years without any symptoms, while others may develop symptoms and decline rapidly over a few months. As HCM progresses, it can lead to heart failure, dangerous blood clots, breathing difficulties, and even sudden death.

Is hypertrophic cardiomyopathy curable in cats?

HCM in cats cannot be cured. However, pet parents can support their cat’s health and quality of life by reducing stress, giving supplements or medications as prescribed by the veterinarian, and choosing a high-quality diet.

IMPORTANT SAFETY INFORMATION

PRN is a trademark of Pegasus Laboratories, Inc. Felycin-CA1 is a registered trademark of TriviumVet, DAC.

CAUTION: Federal law restricts this drug to use by or on the order of a licensed veterinarian. Use only as directed. It is a violation of Federal Law to use this product other than as directed in the labeling.

Felycin-CA1 (sirolimus delayed-release tablets) has been conditionally approved by FDA pending a full demonstration of effectiveness under application number NADA 141-604.

Do not use Felycin^®-CA1 in cats with diabetes mellitus. Discontinue immediately if a cat receiving Felycin-CA1 is diagnosed with diabetes mellitus. Do not administer in cats with pre-existing liver disease. Administration of Felycin-CA1 with drugs that inhibit cytochrome P-450 3A4 or P-glycoprotein, such as calcium channel blockers, amiodarone, azoles, or cyclosporine, may increase risk for toxicity. Use caution when administering in cats with the MDR1 mutation or when administering concomitantly with another P-gp substrate. Treatment with Felycin-CA1 could impact the cat’s ability to mount an adequate immune response to vaccinations.

The use of Felycin-CA1 in cats with viral disease like feline viral rhinotracheitis has not been evaluated. The safety and effectiveness of Felycin-CA1 has not been evaluated in cats with other cardiomyopathy phenotypes, in cats receiving beta blockers or corticosteroids, in cats with kidney disease, hyperthyroidism, or other significant systemic disease. The effectiveness of Felycin-CA1 has not been evaluated in sexually intact cats, therefore, should not be used in animals intended for breeding.

Treatment with Felycin-CA1 has been associated with the elevation of the transaminase enzymes, which include alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Bloodwork should be repeated 1 to 2 months following initiation of treatment, and every 6-12 months thereafter. Discontinue treatment if transaminase values exceed 2X the upper limit of normal (ULN), if other liver enzymes besides ALT or AST are elevated, or if clinical signs of liver dysfunction are noted.

The most frequently observed adverse reactions in cats treated with Felycin-CA1 were cardiovascular in nature, relating to the progression of HCM, and included arrhythmia, congestive heart failure, syncope, and pericardial effusion. Other adverse reactions observed were lethargy, vomiting, diarrhea, and inappetence.

For use only in otherwise healthy cats with subclinical HCM in the absence of other causes of compensatory myocardial hypertrophy (e.g. systemic hypertension), current or historic symptoms of congestive heart failure, arterial thromboembolism, and severe LV outflow tract obstruction.

Not for human use. Keep out of reach of children. Contact a physician in case of accidental ingestion by humans. Pregnant and breastfeeding women should avoid contact with Felycin-CA1. People with known hypersensitivity to sirolimus should administer Felycin-CA1 with caution.

Keep Felycin-CA1 in a secure location out of reach of dogs, cats and other animals to prevent accidental ingestion or overdose.

Felycin-CA1 is conditionally approved by FDA pending a full demonstration of effectiveness under application number 141-604. See prescribing information for complete details regarding adverse events, warnings, and precautions.

References

1. Kittleson, Mark. Hypertrophic Cardiomyopathy in Dogs and Cats - Circulatory System. Merck Veterinary Manual, January 2023. ‌

2. Heart disease in cats (Hypertrophic Cardiomyopathy). Veterinary Teaching Hospital, Washington State University. November 2021.

3. Hypertrophic Cardiomyopathy. Cornell University College of Veterinary Medicine. October 2017.

4. Vandevelde M. Feline Hypertrophic Cardiomyopathy. World Small Animal Veterinary Association World Congress Proceedings, 2004.

5. Cunningham S, Roderick K. Introduction to Heart and Blood Vessel Disorders in Cats - Cat Owners. Merck Veterinary Manual. July 2018.

6. Feline Hypertrophic Cardiomyopathy (HCM). MedVet. December 2016.

7. Kittleson, M. Treatment of Feline Hypertrophic Cardiomyopathy – Lost Dreams. VIN. World Small Animal Veterinary Association World Congress Proceedings. 2014.