Hypertrophic Cardiomyopathy (HCM)
Hypertrophic Cardiomyopathy (HCM): A Complete Patient Guide
Hypertrophic cardiomyopathy (HCM) is an inherited heart muscle condition in which part of the heart wall becomes abnormally thick (hypertrophied), most often the wall between the two lower chambers (the septum). The thickened muscle can be stiff, can obstruct blood flowing out of the heart, and can cause electrical instability. It affects roughly 1 in 500 people and is the most common inherited heart condition.
HCM is usually caused by changes (variants) in genes that make the heart muscle proteins, and is typically passed on in families, with a 50% chance of a child inheriting the gene from an affected parent. Many people have a normal life expectancy and few symptoms, but some develop breathlessness, chest pain, fainting, atrial fibrillation, heart failure or, in a small minority, a dangerous heart rhythm leading to sudden cardiac arrest. HCM is a leading cause of sudden cardiac death in young people and athletes, though this remains uncommon.
The 2023 ESC cardiomyopathy guideline emphasises a structured assessment: confirming the diagnosis, estimating the risk of sudden death, treating symptoms, and offering family screening. Newer treatments, including cardiac myosin inhibitors, have expanded options for people with obstruction.
Symptoms vary widely, even within the same family. Some people are diagnosed after a murmur, an abnormal ECG or family screening and have no symptoms at all.
Common symptoms
Breathlessness, particularly on exertion or on lying flat
Chest pain or tightness, typically with effort or after meals
Palpitations from extra beats or atrial fibrillation
Fatigue and reduced exercise tolerance
Symptoms that need prompt attention
Fainting or near-fainting, especially during or just after exercise
Dizziness on standing up quickly or during exertion
Sustained fast palpitations
No symptoms
HCM may be discovered incidentally, after a family member is diagnosed, or after a screening ECG. A diagnosis does not always mean symptoms or restrictions.
HCM is an inherited condition, in most cases caused by a variant in one of the genes that code for the proteins of the heart muscle (most often MYH7 and MYBPC3).
Genetics
Inherited in an autosomal dominant pattern, so each child of an affected parent has a 50% chance of inheriting the gene
Having the gene does not always mean disease develops, or how severe it will be
Sometimes no family history exists, because a new gene change arose, or relatives have mild disease
Conditions that mimic HCM
Thickened heart walls can also be caused by long-standing high blood pressure, aortic valve narrowing, athletic training, and conditions such as amyloidosis or Fabry disease. Telling these apart matters because treatment differs.
Factors that can make symptoms worse
Dehydration, heavy alcohol, strenuous exertion, large meals, and certain medicines that lower blood pressure or dilate blood vessels may worsen obstruction.
Because HCM can be silent and runs in families, early assessment is valuable.
Arrange a prompt assessment if you have:
A close relative with hypertrophic cardiomyopathy or unexplained sudden death under 50
Breathlessness, chest pain, palpitations or fatigue that are new or worsening
A heart murmur or abnormal ECG that has not been explained
Fainting or dizziness with exercise
A diagnosis of HCM and a change in symptoms, or you wish to play competitive sport
Call 999 immediately if you have:
Collapse or loss of consciousness, particularly during or after exertion
Chest pain lasting more than 15 minutes
Severe breathlessness at rest
Very rapid palpitations with feeling extremely unwell
Diagnosis is made by imaging that shows a thickened heart wall that cannot be explained by other causes. A complete assessment also estimates risk and screens the family.
1. ECG and rhythm monitoring
A 12-lead ECG is abnormal in most people with HCM. Cardiac monitoring over 24 hours to several days looks for atrial fibrillation and dangerous rhythms.
2. Echocardiogram
An echocardiogram measures wall thickness, shows whether blood flow out of the heart is obstructed (at rest and on standing or exercise), and assesses the valves and relaxation of the heart.
3. Cardiac MRI
Cardiac MRI measures wall thickness precisely, detects scarring (late gadolinium enhancement), which contributes to risk estimation, and helps to distinguish HCM from other causes of thick walls.
4. Exercise testing
Stress echocardiography or exercise testing can reveal obstruction that appears only with exertion, assess exercise capacity and the blood pressure response.
5. Genetic testing and family screening
Genetic testing can confirm the cause and allows relatives to be tested for the specific gene change. First-degree relatives are offered ECG and echocardiography, and often repeat screening over time, particularly in adolescence and early adulthood.
Treatment aims to control symptoms, prevent complications and reduce the risk of sudden cardiac death. Many people need no treatment other than monitoring.
Medicines for symptoms
Beta-blockers slow the heart and improve filling, and are usually first choice
Verapamil or diltiazem are alternatives if beta-blockers are not tolerated
Disopyramide may be added for obstruction
Cardiac myosin inhibitors (such as mavacamten) reduce obstruction and improve symptoms in selected people under specialist care
Diuretics may be used for fluid, and anticoagulants are needed for atrial fibrillation regardless of the risk score
Procedures for obstruction
Septal myectomy is surgery to trim the thickened septum, with excellent results in experienced centres
Alcohol septal ablation is a catheter alternative in selected people
Preventing sudden cardiac death
Your cardiologist estimates your 5-year risk of sudden death using a validated risk calculator (HCM Risk-SCD) alongside MRI and other features. If risk is high, an implantable cardioverter-defibrillator (ICD) can detect and treat a dangerous rhythm. The decision is individual and shared.
Advanced disease
A small proportion develop heart failure with a weak or stiff heart, and may need advanced heart failure care, including transplant assessment.
Take your medicines as prescribed and keep regular follow-up with a specialist, usually annually.
Exercise: the 2023 ESC guideline supports regular moderate exercise for most people with HCM, and many can take part in recreational sport and some in competitive sport after specialist assessment and shared decision-making. Discuss your own plan first.
Stay well hydrated and moderate alcohol, as dehydration can worsen obstruction.
Review medicines: avoid unsupervised use of medicines that lower blood pressure or stimulants, and check any new medicine.
Family: encourage first-degree relatives to be screened. Genetic counselling is available.
Pregnancy: most women with HCM have a safe pregnancy, but pre-pregnancy counselling and specialist care are recommended.
Driving: DVLA rules may apply, particularly after fainting or ICD implantation.
Support is available from Cardiomyopathy UK and the British Heart Foundation.
Most people with HCM have a normal or near-normal life expectancy and live active lives, particularly with modern care.
The risk of sudden cardiac death in HCM is low overall and has fallen with risk assessment and ICDs. It is concentrated in a minority who can be identified.
Some people develop atrial fibrillation, which raises stroke risk and is treated with anticoagulation.
A minority progress to heart failure over years, which is why regular review is important.
Outlook depends on the severity and location of thickening, obstruction, scarring on MRI, rhythm problems and family history.
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HCM is an inherited condition of abnormally thick heart muscle, affecting roughly 1 in 500 people, although many are never diagnosed.
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Many people have few or no symptoms and a normal life expectancy.
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Symptoms include breathlessness, chest pain, palpitations and fainting, particularly with exertion.
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It is diagnosed with echocardiography and cardiac MRI, with ECG and rhythm monitoring.
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Each child of an affected parent has a 50% chance of inheriting the gene, so relatives should be screened.
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Beta-blockers are first-line, and cardiac myosin inhibitors, septal reduction and ICDs are options in selected people.
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Risk of sudden cardiac death is assessed individually using validated tools.
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Atrial fibrillation in HCM needs anticoagulation regardless of the usual score.
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Moderate exercise is encouraged for most, with specialist advice on competitive sport.
Guidelines and sources
This page follows current European guidance:
Arbelo E et al. 2023 ESC Guidelines for the management of cardiomyopathies. European Heart Journal 2023;44:3503-3626.
These are the questions patients most often ask about hypertrophic cardiomyopathy.
What is hypertrophic cardiomyopathy?
An inherited condition in which the heart muscle becomes abnormally thick, which can stiffen the heart, obstruct blood flow and cause rhythm problems. It is the most common inherited heart condition.
What are the symptoms of HCM?
Breathlessness, chest pain, palpitations, fatigue and fainting, though many people have no symptoms.
Is hypertrophic cardiomyopathy hereditary?
Yes, in most cases. Each child of an affected parent has a 50% chance of inheriting the gene variant, although not everyone who inherits it develops significant disease. First-degree relatives should be screened.
Can people with HCM live a normal life?
Most can. Life expectancy is normal or near-normal for the majority, and treatment relieves symptoms. Regular follow-up identifies those who need additional treatment.
Can I exercise with hypertrophic cardiomyopathy?
Yes, for most people. Regular moderate exercise is encouraged. High-intensity and competitive sport should be discussed with a cardiomyopathy specialist, because decisions are individualised.
Is HCM a cause of sudden death in young athletes?
It is one of the causes, but sudden cardiac death in HCM is uncommon overall. Screening, risk assessment and ICDs for those at high risk have reduced it.
How is HCM diagnosed?
By echocardiography showing a thick heart wall without another explanation, usually confirmed with cardiac MRI, plus an ECG, rhythm monitoring and sometimes genetic testing.
Do I need a defibrillator (ICD)?
Only some people do. Your cardiologist estimates your 5-year sudden death risk using validated tools and MRI findings. An ICD is recommended if risk is high and may be considered if risk is intermediate.
Can I have a private HCM assessment or family screening?
Yes. A telephone, video or face-to-face consultation in Peterborough or Corby can assess symptoms and family history, with ECG, echocardiography, cardiac MRI and cardiac monitoring arranged as needed.
- How thick is my heart wall, and is there obstruction?
- What is my risk of sudden cardiac death, and do I need an ICD?
- Which medicines are best for my symptoms?
- Should I have genetic testing, and should my family be screened?
- How much and what type of exercise is safe for me?
- Am I a candidate for a myosin inhibitor or septal reduction?
- Do I need rhythm monitoring or anticoagulation?
- Is pregnancy safe for me?
- How often should I be reviewed?
- What symptoms or events should make me seek urgent help?
Left: normal heart. Right: hypertrophic cardiomyopathy, with a thickened septum. Image adapted (cropped and rearranged side by side) from Hypertrophic obstructive cardiomyopathy by Npatchett and BruceBlaus, derived from Blausen.com staff (2014). Licensed under CC BY-SA 3.0.
What changes in HCM
Normal heart: walls of even thickness, relaxed filling and free flow of blood out of the heart.
Hypertrophic cardiomyopathy: a thickened, often asymmetric wall, usually the septum, with stiffness and disorganised muscle cells.
Obstructive HCM: the thick septum and a movement of the mitral valve narrow the outflow channel and can cause a murmur, breathlessness, chest pain or fainting.
Non-obstructive HCM: no outflow obstruction, but stiffness and rhythm risk still need monitoring.
If you have breathlessness, chest pain or fainting, or a family history of hypertrophic cardiomyopathy, you may benefit from a telephone consultation or video consultation, or a face-to-face consultation in Peterborough or Corby for a more comprehensive assessment.
Investigations such as echocardiography, cardiac MRI, ECG reporting and cardiac monitoring may be recommended.
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Medically reviewed by Dr Salam Salloum, Consultant Cardiologist. Last updated: . This page is for general information and does not replace personal medical advice.