Take It to Heart The Ins and Outs of Hypertrophic Cardiomyopathy HCM in Cats

It should be noted Elysian Bengals and its authors are not veterinarians in any capacity. Our information is for education purposes only but should not replace trained professionals and is not responsible for how readers use this information.

As a Breeder Hypertrophic Cardiomyopathy or HCM is something to be quite aware of; not only to understand what HCM is, but also concerning the breeders you are working with, buying cats from, how to screen for it, what to look for in the final report, and how to publicly deal with a positive result. As a kitten buyer, it is equally as important to know what HCM is as well as how breeders should be handling its prevention and diagnosis to ensure you are supporting ethical breeders and getting the healthiest kitten you can.

Hypertrophic Cardiomyopathy, or HCM, is a common disease, not only in purebred cats, but also in those of mixed ancestry. It affects approximately 15% of the cat population (1), with higher risk in specific breeds, as well in male cats (at a 3:1 ratio) (2). There is also a higher population of mixed breed cats than purebred cats (3). The most common cat breeds afflicted by this disease includes (4): Bengal


Maine Coon

Sphynx (5)



British Shorthair (6)

The condition affects the heart causing an enlargement and thickening of the heart wall, specifically the left ventricle. The left ventricle is responsible for being the main pump system in the body (7, 8). This can greatly alter the function of the heart, causing abnormal heartbeats and improper uptake or lack of oxygen. Furthermore, as the main center for pumping blood, the function of the lungs can be affected and blood clots can develop. Blood clots are one of the most concerning symptoms. These blood clots can break off and travel along the arteries eventually settling and blocking the proper flow of blood in the body. This can be so severe that a blockage causes paralysis, most often in the hind limbs. This event can seem quick and effect the cat immediately. Finally congestive heart failure often results, eventually leading to death.

Many cats live with heart diseases without symptoms. Unfortunately, symptoms typically don’t appear until the condition is fairly far along. Common symptoms one can see include getting winded easily, lethargy, and having trouble breathing (including open mouth breathing). At this point fluid around the lungs has affected their normal function. Symptoms can be exacerbated by stress, surgery under anesthesia, even fluids or pharmaceutical drug treatments.

If caught early enough, and with treatment, many cats are able to live a full, quality life.

7% of cats with onset signs of HCM will typically develop heart failure by 1 year of age, 20% by 5 years, and 25% within 10 years (9). These statistics are regardless of the size of the left atrium.

Of these cats, once in heart failure, 50% pass away within 2 months. For those that suffer a blood clot, 70% pass within a week. In other studies 37% of cats survived to 11.5 months and 20% survived to 4 years (10, 11).

A cat can be born with HCM or develop it as an adult later on in life. While HCM isn’t 100% understood, it is, in part, a genetic condition.This disease is hereditary in origin, as certain proteins mutate causing the wall thickening. In the Sphynx (12), Ragdoll (13) and Maine Coon (14) breeds, several gene markers have been identified and can be tested for.

For the breeds that do have genetic markers, the understanding is that a cat with no copies of the gene will not develop HCM; those with one copy are at risk for developing HCM, and those with two copies will develop the disease. This type of genetic inheritance is known as autosomal dominant. Autosomal means that the gene is located on a chromosome that is not a sex chromosome. Dominant means that only a single gene is required to cause the disease, compared to recessive, where the cat would always need two copies of the gene to cause the disease.

While a species-appropriate raw diet is ultimately the best diet for our carnivore companions and supports a happy, healthy heart, thus far diet is not a contributor to the development of HCM (15).

Excessive growth hormone and parathyroid hormones are other genetic causes of the disease.

While there are a few genetic tests for some breeds, there seems to be many variants and genes for HCM, so while some of these genetic tests can help identify carriers or affected/future affected cats, they are not 100% encompassing. An echocardiogram, or ultrasound of the heart, is the best preventative way to monitor the heart over time. An echocardiogram, through ultrasound waves, creates an image of the heart. A cardiologist is able to not only measure the heart, but also view the blood flow and take note of how the valves are functioning. Over time they are able to monitor the heart’s growth, as well as listen for murmurs, which indicates a restriction of blood through the heart.

This screening is not a guarantee a cat will never develop HCM, it is simply a precautionary practice. Early detection means earlier treatment and a better chance at a higher quality of life.

Breeding cats should be screened every year to year and a half. Reputable breeders will not only do these screens but will also provide the results for each cat. Unless one suspects HCM in a juvenile cat, screenings should not begin until the cat is at least 1 year old. Up until this point the heart is still growing and results may be inaccurate. Breeders and owners should then continue screening every 1-1.5 years.

As mentioned prior, many cats live asymptomatically. When symptoms start to appear, it is often too late. This is why yearly screenings are absolutely essential. It is the only way we can detect early signs of HCM in the hopes to prevent, or catch and treat the condition, to give our cats the best possible chance at a normal and long life.

First, other diseases should be ruled out including hyperthyroidism, high blood pressure, acromegaly (growth hormone abnormalities), and dehydration. Once other diseases are ruled out, the following is evaluated via M-mode and 2-D Echocardiograms methods. 1. Determine Left Ventricle enlargement (hypertrophy)

2. Determine LVOT obstruction (Left Ventricle Outflow Tract) - this looks at the blood flow out of the ventricle into the arteries

3. Evaluate SAM (Systolic Anterior Motion) - an LVOT obstruction creates a narrow pathway

due to the enlarged ventricle and papillary muscles. These muscles help prevent leakages between the atrium and ventricles when blood is being pumped from the heart chambers into the arteries (16, 17). This event is typically what is identified as a heart murmur.

4. Evaluate the contractions and emptying of the left ventricle (systolic) and the refilling of the left ventricle (diastolic) after systole of blood and oxygenation.

5. The size of the Left Atrium should also be measured and evaluated. In addition to size measurement, the ratio between the left atrium and aorta is also used to evaluate the Left Atrium (18). Typical ratios measure at <1.6 mm but when larger than 1.8-2.0 mm it is determined this cat will most likely develop heart failure or arterial thromboembolism (a blood clot causing a blockage in an artery) (19, 20).

There are two reliable methods for HCM diagnosis, typically used in conjunction with each other. An M-mode echocardiogram, where the M stands for movement or motion, is a chart or diagram of how the heart and its structural parts function through its cardiac cycle.