American Shorthair HCM: Symptoms, Early Detection, and Age-Specific Care Guide

HeartBreed HealthMeongsiljang Veterinary Advisory Board

American Shorthairs are a breed at high risk for hypertrophic cardiomyopathy (HCM). We’ve outlined age-specific screening schedules, signs to watch for at home, and everything from diagnosis to treatment.

American Shorthairs and Hypertrophic Cardiomyopathy

Important considerations for hypertrophic cardiomyopathy in American Shorthair cats

Hypertrophic cardiomyopathy (HCM) is the most common heart muscle disease in cats, characterized by abnormal thickening of the heart muscle. Family history and breed predisposition are considered risk factors, so it’s important to monitor heart health throughout an American Shorthair’s life. The most critical point is that early stages often show no visible symptoms. By the time signs like difficulty breathing or loss of appetite appear, the condition has often progressed significantly. Therefore, even in the absence of symptoms, regular cardiac ultrasound examinations in consultation with your veterinarian are essential for proper management.

What Is Hypertrophic Cardiomyopathy (HCM)?

Hypertrophic cardiomyopathy (HCM) is a heart disease in which the left ventricular wall becomes thickened and stiff, impairing the heart’s ability to relax and fill with blood. When the left ventricle cannot expand properly, pressure builds up in the left atrium and subsequently in the pulmonary veins, creating a vicious cycle. Additionally, the thickened muscle narrows the heart’s internal chambers, leading to blood stasis and the formation of blood clots. If a clot blocks a blood vessel, it can cause hindlimb paralysis or sudden respiratory distress (arterial thromboembolism). HCM is a known familial (genetic) condition, with the risk of onset typically increasing in middle-aged and older animals.

A veterinarian performing an echocardiogram on a cat.

Heart Testing Is Needed If You Notice These Symptoms

Rapid breathing: Even while resting or sleeping, your cat’s breathing becomes faster than usual, with noticeable abdominal movement.

Reluctance to move: Your cat avoids climbing to high places and shows reduced overall activity.

Decreased appetite: Your cat suddenly leaves food uneaten or skips meals entirely on repeated occasions.

Open-mouth breathing: This is an unusual sign of respiratory distress in cats and requires immediate veterinary attention.

Rear leg abnormalities: If your cat suddenly drags its hind legs or they feel cold and weak, suspect arterial thromboembolism.

Go to the 24-Hour Emergency Clinic Immediately

If your pet is breathing rapidly with its mouth open, or if its gums and tongue have turned blue, immediate emergency care is required. Sudden inability to use the hind legs, along with cold limbs and signs of pain, indicates a cardiac thrombus (arterial thromboembolism). Both conditions can be life-threatening within hours, so you must go to an emergency clinic immediately, regardless of whether it is night or early morning.

Age-Specific Lifelong Care Points

Under 2 years (kitten/growth stage): Conduct a basic health checkup and listen to the heart with a stethoscope to check for murmurs. 3–5 years (early adulthood): Have a baseline heart ultrasound at least once. If no abnormalities are found, establish a follow-up schedule with your veterinarian. 6–9 years (middle age): Regularly monitor blood pressure alongside heart ultrasounds. 10 years and older (senior): We recommend regular comprehensive checks including heart ultrasounds, blood tests, and chest X-rays. Even in the early stages of HCM, if there are no symptoms, medication may not be immediately necessary, and regular monitoring alone may be sufficient. Establish examination intervals and management plans in consultation with your veterinarian.

Age-specific health care for American Shorthairs, from kittens to seniors

HCM Diagnostic Methods

Echocardiography (echo) is the gold standard for diagnosing HCM, as it allows direct measurement of left ventricular wall thickness. If a heart murmur is detected during auscultation, echocardiographic confirmation is necessary. Blood tests for cardiac stress markers (NT-proBNP) may also be used for screening purposes. Thoracic radiographs help assess whether fluid has accumulated in the lungs (pulmonary edema). After diagnosis, we recommend consulting with a board-certified veterinary cardiologist for further guidance.

HCM Treatment and Home Care

Treatment for hypertrophic cardiomyopathy (HCM) varies depending on the stage of the disease. In the early stages, when there are no symptoms, regular monitoring is maintained. If the heart rate becomes rapid or respiratory abnormalities occur, medications to control heart rate or diuretics may be prescribed. If there is a risk of blood clots, anticoagulants may be used in combination. The type and dosage of medication depend on the pet's weight and examination results, so do not change or stop the medication without consulting your veterinarian.

A veterinarian listening to a cat's heart with a stethoscope

Regular Heart Ultrasounds: How to Plan

Even if your American Shorthair hasn’t been diagnosed with HCM, regular heart ultrasounds are recommended after they reach adulthood if there’s a family history or breed predisposition. If your cat has already been diagnosed with HCM, it’s important to follow up with regular check-ups as scheduled by your veterinarian. At home, it’s also helpful to monitor your cat’s resting breathing rate while they’re sleeping to ensure it hasn’t increased. If you notice repeated episodes of rapid breathing, contact your vet right away.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Do all American Shorthairs inevitably develop hypertrophic cardiomyopathy (HCM)?

Not at all. Even with a family history or breed predisposition, not every dog will develop the condition. Early detection through regular cardiac ultrasounds makes management much easier.

What is the life expectancy after an HCM diagnosis?

If caught early while your cat is still asymptomatic, they can live close to their natural lifespan. While progression to heart failure or blood clots can impact longevity, many cats maintain a good quality of life with consistent medication and regular follow-up examinations.

Is there a way to check the respiratory rate at home?

To check your cat’s breathing rate, count the number of chest rises and falls over 60 seconds while they are sleeping and relaxed. If you notice repeated episodes of faster-than-normal breathing, contact your veterinarian. Keeping a log of the date and respiratory rate in your smartphone’s notes can help you quickly spot any changes.

Are there any foods or supplements that are good for HCM?

There is no definitive evidence that any specific diet can prevent hypertrophic cardiomyopathy (HCM). Since taurine deficiency can cause cardiomyopathy, feeding a balanced, complete diet is essential. If you are considering omega-3 supplementation, please consult your veterinarian first.

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References

[1] Luis Fuentes V, Abbott J, Chetboul V et al., ACVIM Consensus Statement Guidelines for the Classification, Diagnosis, and Management of Cardiomyopathies in Cats, J Vet Intern Med, 2020

[2] Meurs KM, Sanchez X, David RM et al., A cardiac myosin binding protein C mutation in the Maine Coon cat with familial hypertrophic cardiomyopathy, Hum Mol Genet, 2005

[3] Fox PR, Oyama MA, Reynolds C et al., Utility of plasma N-terminal pro-brain natriuretic peptide (NT-proBNP) to distinguish between congestive heart failure and non-cardiac causes of acute dyspnea in cats, J Vet Cardiol, 2009

[4] Fox PR, Oyama MA, Textbook of Cardiovascular Medicine in Dogs and Cats, 2020