About HCM

What is Feline Heart Disease-Especially HCM

Unless a heart murmur is the first thing diagnosed in a cat, usually heart disease is diagnosed when the cat is unable to breathe.  Many pet owners may not have noticed that for a few days leading up to the moment they noticed the cat's inability to breathe, that the cat may not have been eating well, or may have been lethargic, or looked as if uncomfortable or in pain, or may have had to stop and rest often while walking or running, or may have been breathing rapidly while resting.  A cat that is breathing rapidly in distress, will have while sleeping or while resting but not sleeping, rapid chest (or center of the body) heaving movements.  It is rare that a cat will cough or will pant with its mouth open while in breathing distress but those should not be dismissed either.  Another common sign that pet owners encounter is finding the cat is suddenly having a heart attack or a lame/paralyzed limb.  These are caused by a blood clot that has formed in the heart and broken away and traveled through the body.  Sometimes, pet owners come home and find that the cat has suddenly died. 

In general, there are four types of heart disease seen in cats: HCM-hypertrophic cardiomyopathy, RCM-restrictive cardiomyopathy, DCM-dilated cardiomyopathy, and ARVC-Arrhythmogenic Right Ventricular Cardiomyopathy.   While each affects the heart function differently and may have unique symptoms, all four affect the ability of the heart to fully function, can lead to congestion and impaired breathing ability, blood clots, heart attacks, and  eventually death.    

They share many of the same symptoms and the medications used to treat the disease.

While HCM and heart disease leads to death, the progression of the disease varies from patient to patient depending on the type of heart disease, the age of the cat at first incident or diagnosis, if the disease was discovered before the cat became ill of the effects of the disease or whether  CHF or a heart attack or a blood clot occurred first, and the effect of the medications upon the disease.   Some cats will be diagnosed while a kitten and may die young while others will live for years-either with few symptoms or issues or complications or with many symptoms, issues, and complications.  Some cats will be free of the disease while young but will have the disease appear around the age of 8-18 and will have a couple of years or a few years left.   The ability of a cat to live with heart disease for any length of time depends on a pet owner's vigilance, medication therapy, and quality vet care, as well as the general health of the cat.   Controlling congestion, decreasing the likelihood of clots, and keeping the cat free of stress will go a long way in managing the progression of the disease and the effects of the disease on the cat. 

"Hypertrophic" means thickened, where the walls and ventricles of the heart become too thick, or hypertrophied, making it difficult for the heart to fully function and contract or pump blood. Other diseases also cause thickening of the left ventricular wall, including aortic stenosis, hyperthyroidism, and high blood pressure.  

There are many breeds to which HCM is prevalent: Maine Coon, Sphynx, Ragdoll, Siberian, etc.  But it also includes the regular house cat so basically, almost any cat is a potential victim of heart disease.

Damage to the Heart

As HCM progresses, the actual structure of the heart changes and heart function is affected. Thickened muscle walls become less flexible, and the left ventricle can no longer relax or stretch efficiently to fill with blood.

These changes can create a heart murmur because the heart valves don't grow as the heart muscle enlarges.  Some cats will develop a heart murmur that is caused by SAM-systolic anterior motion in the mitral valve.  When a heart murmur is present, it usually can be heard and that is when the vet will recommend further testing to rule out the cause of the murmur.  Some cats will have heart murmurs that are stress related but the majority of heart murmurs are heart disease related.  Any known heart murmur must be properly diagnosed so that treatment can begin in time.  Do NOT go by what a vet may say about the "size" of a murmur, that it is "only" a 1 or 2 or...and can be ignored or that the size means that heart disease isn't present.  The size of the murmur is not indicative of the extent of heart disease nor a sign of the type of disease present. And since it can be stress related, may not even indicate the presence of heart disease.  A visit to a cardiologist for xrays and an echo will be needed.  

As the heart muscle walls thicken, as the heart beats, not all of the body's fluid (blood and water) can be taken into the valve when the heart valve opens.  As the heart valve closes, the extra or remaining fluid backs up into the lungs or chest cavity, leading to congestion or congestive heart failure.  This is a dangerous time as the congestion leads to breathing difficulty.  Left too long, with the cat in breathing distress, the lungs will fill with fluid and the cat will die of the inability to breathe. 

As the heart is beating, and after the valve has opened to receive the body's fluid, the heart valve closes and then opens again. This process of opening the valve means it is pushing out the fluid it took in, causing the fluid to go into circulation in the body.   As the heart walls thicken due to disease, there is less ability for the heart to pump out of the valve the fluid, leading to blood pooling in the valves. This pooling blood can lead to the creation of clots which can break away from the interior of the heart and block an artery in either the heart-leading to a heart attack-or a leg, either of which will be painful and potentially deadly (clots may settle in other arteries but the heart and legs are the most likely in cats.)

Diagnosis of HCM

If heart disease is suspected, a visit to a vet cardiologist is necessary.  The cardiologist will take xrays to look at the condition of the lungs and to see if the lungs are congested.  The size of the heart can also be noted on the xrays but only if the heart is thickened enough as to enlarge it.  The cardiologist will perform an echo or ultrasound which will show how well the heart is functioning, if there are clots, how thick any valves may be, and how extensive is the damage to the heart, and which type of heart disease is present.  Blood work known as a CBC/chem panel must be done to see what is the overall health of the body and the effect of heart disease on the body. 

While there is a blood test to test for an HCM gene, the test does not indicate whether HCM or other heart disease is present at a given moment, only that it is genetically possible.  Nor does a blood test tell of the extent of the damage if disease is present.  An echo is needed even if the gene test is positive.  Since the blood test is expensive, unless an owner intends to breed with the cat, the owner-if worried about a cat having heart disease-should see a cardiologist for xrays and an echo. 

Treatment Options for Cats with HCM

There are many different types of medications that can be given to a cat depending on severity of the disease. (See the Med tab for further information.)

Lasix is a diuretic and is necessary to rid the body of extra fluid and to control the level of fluid in the body. Will help prevent or decrease the ability of CHF to form and will aid in the breathing function.

 ACE inhibitors such as enalapril, slow the heart rate and lower blood pressure and keep blood veins from being constricted.

Beta blockers such as atenolol slow the heart rate and help lower blood pressure.

Plavix and aspirin act as blood thinners which decreases the chance of a blood clot forming; thinner blood lessens the work of the heart.

Spironolactone acts as a diuretic and helps to preserve much needed potassium which is necessary for kidney function.  

A cat with heart disease and which is on meds, needs a good overall vitamin made for cats.  

Other supplements that aid in heart health are amino acids (those formulated only for cats), and COQ10.  Potassium supplements (cats may take almost any form made for humans but check the brand or type with your vet) will increase the blood potassium levels that usually fall due to the much needed lasix.   The vet will do a CBC/chem blood panel from time to time to check the body's function and overall health as well as the effects of medications on the liver and kidneys. The results  should always be reviewed with the vet and any levels too high (hyper) or too low (hypo) should be discussed.

Other Types of Heart Disease

 Dilated cardiomyopathy results in heart chambers that are dilated in size.  It was once a common heart disease in cats and was caused by a lack of taurine in a cat's diet.  Once commercial cat food was made with taurine, the disease almost disappeared.   Now it is rarely seen.  If diagnosed, it is either due to homemade diets that lack taurine or could still be possibly genetic.  Cats with dilated cardiomyopathy that is due to taurine deficiency generally respond well to supplementation with taurine but any damage that was caused may not be reversible.  Drugs used to treat dilated cardiomyopathy are similar to those used in hypertrophic cardiomyopathy.

In restrictive cardiomyopathy, the heart muscle in the ventricle of the cat contains a large amount of fibrosis or scarred tissue.  This results in the ventricles being stiffer than normal, making it more difficult for them to contract normally. This leads to a failure of the heart's ability to pump blood effectively.  Symptoms of restrictive cardiomyopathy in cats are similar to those seen with other cardiomyopathies.  But usually, RCM cats get congestion in the chest cavity as well as the lungs and must have fluid withdrawn from the body.  They may be given many of the same drugs as with HCM.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a form of cardiomyopathy that affects the right side of the heart. Symptoms are those of right-sided heart failure, including ascites (fluid in the abdominal cavity) and swelling in the legs.  An arrhythmia (abnormal heart rate or rhythm) may also be present. 





Websites with Information Regarding HCM

Online Merck Vet Manual

Harpsie-a person's website about their HCM cat experience that discusses felinediseases with links to further information.

A vet's website regarding HCM in cats.

A link to Long Beach California vet hospital's discussion re: HCM. Useful terms, descriptions, and illustrations.

Washington State University College of Veterinary Medicine

An older site from around 2007 with basic information and drawings and details.

A pamphlet with HCM information. 

PetMD offers HCM information as well as general cat health information.

Cornell University College of Veterinary Medicine

University of Minnesota has a page with definitions and 3D imaging about the heart


Knowing and using medical terms will help you better discuss issues with the vet:

Medical terms to know.

Know, understand, and how to use medical measuring/dosing terms such as "q", "TID", etc. 

This site offers information about understanding blood chemistry values.

A good source for definitions and terms relating to the heart and heart disease


A pet owner must be aware of many things affecting a cat that has heart disease:

A post about a HCM check-up and a discussion about how HCM can be misdiagnosed, with information about HCM, and other information.

How to tell if a cat has a blood clot in the leg. 

Issues to watch for in a HCM cat

Different types of congestion may occur in cats with heart disease:

Pulmonary edema-fluid buildup in the lungs.  It leads to impaired gas exchange and may cause respiratory failure. Treatment is focused on three aspects: improving respiratory function, treating the underlying cause, and avoiding damage to the lung. Pulmonary edema, especially in the acute setting, can lead to respiratory failure, cardiac arrest due to hypoxia and death. Low oxygen saturation and disturbed arterial blood gas readings support the proposed diagnosis.  Echos may strengthen the diagnosis by demonstrating impaired left ventricular function, high central venous pressures and high pulmonary artery pressures. The causes of pulmonary edema can be divided into cardiogenic and non-cardiogenic. By convention cardiogenic refers to left ventricular causes. Non-cardiogenic are varied and can include hypertensive due to a combination of increased pressures in the right ventricle and pulmonary circulation and also increased systemic vascular resistance and left ventricle contractility increasing the hydrostatic pressure within the pulmonary capillaries leading to extravasation of fluid and edema.   Patient is given oxygen and diuretics and other heart meds to manage any heart conditions and to stabilize the heart.

Pleural effusion-fluid buildup around the lungs in the pleural cavity, easier to aspirate-withdraw with a needle. This procedure is done every few weeks. The cat will feel better for 2-3 weeks before beginning to feel poorly again, at which point, the cat needs to see the vet again.    Symptoms might include coughing, difficult breathing, increased rate of breathing, cat cannot sit comfortably, and may or may not have open mouth breathing.  Might also have a lack of energy and a lack of appetite.