HCM in Sphynx cats. Why are regular heart scans so important?

© Agnieszka Mianowska · Aggio Cat*PL · aggiocat.pl

HCM (hypertrophic cardiomyopathy) is a disease of the heart muscle that can develop in a cat for a long time without visible symptoms. Sphynx cats are among the breeds in which it must be taken particularly seriously. A cat seeming well, normal findings when listening to the heart, or even a previous normal examination therefore do not remove the need for further checks.

Key points

• Echocardiography is the main examination used to diagnose and monitor HCM.
• The absence of a murmur does not rule out disease. A cat with HCM may behave completely normally.
• ALMS1 is not a confirmed HCM marker in Sphynx cats. Subsequent studies have not confirmed its usefulness in assessing disease risk.
• Up-to-date heart scans of the parents matter. In a responsible breeding programme, they should be performed at least once a year.

What actually happens to the heart in HCM?

A healthy heart must not only contract to pump blood but also relax and fill freely between beats. In HCM, the muscle of the left ventricle thickens, and its walls may become less able to relax. This makes ventricular filling more difficult and may increase pressure in the left atrium.

Some cats remain symptom-free for many years. Others develop left atrial enlargement, heart failure or a blood clot that can block blood flow to the limbs. HCM does not automatically mean a short life, but it requires an individual risk assessment.

HCM should also be distinguished from other heart diseases. Not every murmur, valve defect or congenital structural abnormality means hypertrophic cardiomyopathy.

HCM is the most commonly diagnosed heart disease in cats. Its causes are not fully understood, but higher occurrence in some breeds and families, together with the discovery of HCM-associated genetic variants in Maine Coons and Ragdolls, indicates that heredity plays an important role. This does not mean that there is one universal genetic test for every breed. In Sphynx cats, regular heart examinations and information about relatives’ health are particularly important.

Even if both parents have normal heart examination results, later development of HCM in their offspring cannot be completely excluded. HCM may be diagnosed only when a cat is several years old, despite earlier normal scans. The age at diagnosis alone cannot establish the cause or confirm a hereditary basis.

Not every thickened heart wall is HCM. Similar changes can result from conditions such as hypertension or hyperthyroidism, particularly in older cats. Appropriate diagnostic investigation is therefore needed to establish the diagnosis and possible causes.

Why are regular heart examinations important for Sphynx cats?

HCM occurs in both pedigree and non-pedigree cats. Breeds at increased risk, besides Sphynx cats, include Ragdolls, Maine Coons and British cats. A study published in 2024 followed 55 apparently healthy Sphynx cats in New Zealand, with some undergoing repeat echocardiography about two years later. HCM was ultimately diagnosed in 40% of the cats studied. This finding supports regular screening but must not be treated as the prevalence among all Sphynx cats.

In three cats from this group that died of heart failure, post-mortem examination found extensive myocardial ischaemia or infarction. Such a small number of cases does not establish infarction as a typical cause of death in Sphynx cats with HCM. Disease may become apparent only in adulthood, so a normal scan in a young cat does not mean it will remain unaffected later. Regular examinations and the health history of parents and older relatives therefore matter.

Echocardiography: what does the cardiologist assess?

Echocardiography, or cardiac ultrasound, provides a detailed view of heart structure and assesses function in real time. The veterinarian measures wall thickness and chamber size, checks muscle contraction and relaxation, and uses Doppler imaging to assess blood flow. This is the main examination used to diagnose feline HCM. The cardiologist assesses factors including:

• left ventricular wall and interventricular septal thickness and whether thickening is uniform;
• left atrial size, which is particularly important when assessing complication risk;
• valve function and blood flow, including possible dynamic left ventricular outflow tract obstruction;
• overall heart function, considering the clinical picture and previous examinations.

The report may contain abbreviations such as IVSd, LVPWd/LVFWd, LA/Ao or SAM. These are components of a full assessment, rather than separate ‘positive/negative tests’.

Does every wall thicker than 5.5 mm mean HCM? No. Thickness must be interpreted in relation to body weight, age, hydration, measurement technique, the appearance of other structures and other possible causes of hypertrophy. ACVIM guidance notes that many cats have a normal left ventricular wall below 5 mm, while 6 mm or more raises strong suspicion of hypertrophy. Intermediate results need particularly careful interpretation. A diagnosis should not be based on one number.

It is also important to check whether thickening results from other diseases, particularly hypertension or, in older cats, hyperthyroidism. Blood tests for NT-proBNP and cardiac troponin I (cTnI) can also help. NT-proBNP is a protein fragment released when the heart walls are excessively stretched or strained. It can help detect more advanced heart disease or determine whether breathing difficulties have a cardiac cause. A normal result does not, however, exclude mild or early HCM. Troponin I is a protein released into the bloodstream when heart muscle cells are damaged. An increased concentration may provide information about myocardial injury and prognosis and, in some circumstances, help distinguish cardiac from other causes of breathing difficulty. Neither marker diagnoses HCM on its own or replaces echocardiography.

Why does the cardiologist ask about diarrhoea, vomiting or dehydration? Fluid loss can reduce ventricular filling, making the walls appear thicker on ultrasound. This is called pseudohypertrophy, which can resemble HCM without a true increase in heart muscle mass. The veterinarian therefore needs to know the cat’s current health, medications and hydration problems. For routine screening, they may recommend postponing the examination until the cat has recovered.

What if the veterinarian hears a murmur? A murmur warrants further investigation but does not itself mean HCM. In cats, it can result from various blood-flow abnormalities, sometimes including dynamic right ventricular outflow tract obstruction (DRVOTO), which is also seen in cats without structural heart disease. HCM, in turn, may involve dynamic left ventricular outflow tract obstruction (DLVOTO), often associated with systolic anterior motion of the mitral valve leaflet (SAM). Echocardiography with Doppler assessment establishes the source of the murmur and whether heart muscle disease is also present.

© Agnieszka Mianowska · Aggio Cat*PL · aggiocat.pl

What does the scan mean? More than wall thickness

Two female cats may have similar heart muscle thickness measurements but very different prognoses. The cardiologist considers not only whether hypertrophy is present but also how the heart fills, whether the left atrium is enlarged and whether there are signs of increased clot or heart-failure risk. The term ‘HCM’ is therefore not equivalent to a diagnosis of advanced disease.

ACVIM disease stages

• Stage A: the cat has risk factors, but examinations show no cardiomyopathy. A healthy relative of a cat with HCM may fall into this stage.
• Stage B1: heart disease is evident on examination, but the cat has no symptoms and the risk of near-term complications is considered low.
• Stage B2: the cat may still appear completely healthy, but findings indicate a higher risk of heart failure or thromboembolism. Left atrial size and function are particularly important.
• Stage C: signs of heart failure or a thromboembolic complication have occurred, even if treatment has brought them under control.
• Stage D: heart failure is resistant to standard management.

In practice: ‘HCM, no symptoms’ does not tell the whole story. Ask the cardiologist about the current stage, whether the left atrium is normal and when the next scan is needed. Do not apply this staging system yourself on the basis of individual report values.

Breeding-cat screening: what standard should apply?

Breeding Sphynx cats should have echocardiography at least once a year. The first examination is planned after 12 months of age and before breeding begins. At each subsequent mating, the cat should have an up-to-date result no more than 12 months old. If there is a family history of HCM, an earlier result was equivocal or the cardiologist identifies other reasons, examinations may be needed more often, even every six months.

Why is this so important? HCM may appear only after years of normal results and does not always produce noticeable symptoms. A scan performed five years ago documents the heart’s condition five years ago, not today. Keep successive reports and also consider the health of breeding cats’ parents, siblings and older offspring.

What will change in FIFe from 1 January 2027?

At the FIFe General Assembly in May 2026, a new provision was adopted: § 6.26. From 1 January 2027 every Sphynx must, before first being used for breeding in FIFe, have had at least one heart ultrasound showing no abnormalities, performed by a qualified veterinary cardiology specialist. This rule also applies to FPL catteries.

This is an important step, but it is necessary to distinguish a regulatory requirement from good practice. At this stage, FIFe requires one examination before breeding begins, rather than annual repeat scans. A responsible breeder should not stop at the regulatory minimum, because a result describes the heart on the examination date, rather than for the cat’s lifetime.

What should you ask before buying a kitten?

Ask to see current echocardiography reports for both the kitten’s mother and father. Check the examination date and the identity of the cat examined. At the time of mating, each parent’s result should have been no more than a year old. Also ask about examinations in earlier years and the health of older relatives.

If a breeder avoids showing results, cannot provide the examination date or presents one old scan as proof of lifelong heart health, treat this as a serious warning sign. It is better to decide against buying than to accept assurances that cannot be verified.

At Aggio Cat*PL we regularly examine our breeding cats’ hearts, adapting the frequency to age, family history and the cardiologist’s advice. I believe a transparent screening history matters more than a single assurance that ‘the cat is healthy’.

ALMS1: why did the DNA test fall short of breeders’ expectations?

For a time, Sphynx breeders had high hopes for the discovery of a variant in the gene ALMS1. It was hoped that DNA testing would identify cats particularly at risk of HCM, helping reduce the disease more effectively within the breed.

Subsequent scientific studies did not, however, confirm a significant association between the tested ALMS1 variant and HCM diagnosis in Sphynx cats. In the 2024 New Zealand study, the variant occurred in about 71% of the cats tested, regardless of disease status. A study of the Sphynx population in Thailand, published in 2026, reached similar conclusions.

Although some laboratories still offer ALMS1 testing as an HCM-related test for Sphynx cats, current evidence does not support its usefulness in predicting this disease or making breeding decisions. An ALMS1 result alone should not be presented as proof of heart health or a measure of breeding quality.

The ALMS1 story shows why genetic test results must be interpreted in the light of subsequent independent publications. An association proposed in earlier research did not become a reliable screening tool for Sphynx cats. It must not be used to label kittens ‘HCM-free’ or to make breeding decisions solely on this DNA variant.

This does not negate HCM’s hereditary nature. It simply means that there is currently no reliable DNA test for Sphynx cats that establishes an individual’s risk of this disease. Responsible preventive care continues to rest on regular echocardiographic examinations and knowledge of the health history of whole cat families.

Can a cat have heart disease without any symptoms?

Yes. Early or moderate HCM often produces no signs an owner would notice. Some cats also have no audible murmur. Listening to the heart during a routine appointment is therefore not equivalent to echocardiography.

Reduced exercise tolerance, unusual hiding, reduced appetite, weakness or fainting require veterinary assessment. These signs can have many causes, not only cardiac ones.

Warning signs: when is urgent help needed?

• Open-mouth breathing, obvious breathlessness, increased breathing effort or blue mucous membranes: immediate veterinary help.
• Sudden, painful weakness or paralysis of one or both hind limbs: an emergency, possibly an arterial thromboembolism.
• Fainting, collapse or sudden severe weakness: urgent veterinary assessment.

At home, you can monitor breathing rate during peaceful sleep. In many healthy cats, it is around 15–30 breaths per minute. Persistent rates above 35 breaths per minute need veterinary advice; if breathing is visibly difficult, do not count breaths or wait for improvement. Arrange help immediately.

© Agnieszka Mianowska · Aggio Cat*PL · aggiocat.pl

What does an HCM diagnosis mean for a cat?

HCM treatment depends on disease stage and the cat’s health. Not every diagnosed cat needs medication immediately. Some cases require regular cardiology checks; others need treatment tailored to specific abnormalities and symptoms. Research into new therapies is also ongoing.

There is no single diet, supplement or home method that prevents HCM. Appropriate nutrition, a healthy body weight and management of other diseases support overall health but do not replace heart examinations.

Further management depends on disease severity, left atrial size, any blood-flow abnormalities and thromboembolic risk. A symptom-free cat and a cat with heart failure need very different care plans. Not every HCM diagnosis means immediate medication is necessary.

Frequently asked questions

Do normal parental heart scans guarantee that a kitten will remain unaffected? No. Well-documented preventive screening reduces uncertainty but cannot provide a lifetime guarantee for offspring.

Does HCM occur only in breeding cats? No. Neutered cats can also develop it. Being part of a breeding programme or a household companion makes no difference to a cat’s need for health care.

Is a cat without a heart murmur healthy? The absence of a murmur is good news but does not rule out HCM. Echocardiography is needed when disease is suspected and for breeding screening.

Can you have one heart scan and consider the matter settled? No. HCM may become apparent only with age. Responsible breeding practice involves echocardiography at least once a year, even though FIFe’s rules from January 2027 require only one examination before breeding begins.

Should the breeder show both parents’ heart scans? Yes. A prospective owner should be able to see reports with dates and cat identification. At mating, the result should be no more than 12 months old. If a breeder refuses to share this information, consider looking for another cattery.

Does a normal NT-proBNP result rule out HCM? No. The biomarker can support risk assessment or diagnosis, but it remains normal in some cats with asymptomatic HCM. Echocardiography is decisive.

What should you remember?

The best protection against missing HCM is informed, consistent preventive screening. This is not a promise that no cat will ever become ill. The aim is to detect abnormalities as early as possible, respond appropriately and make responsible decisions about animal health and breeding.

Further information

• ACVIM guidelines on diagnosing and staging feline cardiomyopathies
• Study of HCM and the ALMS1 variant in Sphynx cats in New Zealand (2024)
• ALMS1 study in Sphynx cats in Thailand (2026)
• FIFe: breeding-rule changes from 1 January 2027

© Agnieszka Mianowska · Aggio Cat*PL · aggiocat.pl