Hypertrophic Cardiomyopathy

Authored by , Reviewed by Dr Louise Newson | Last edited | Certified by The Information Standard

Hypertrophic cardiomyopathy (HCM) is a condition where the heart muscle becomes thickened. The symptoms that develop depend on the severity of the condition. The treatment depends on the type of symptoms you have and whether there are any complications. Some people need no treatment. Most cases are hereditary so screening of close family members is recommended.

The heart has four chambers - two atria and two ventricles. The walls of these chambers are mainly made of specialised heart muscle called myocardium. During each heartbeat both of the atria squeeze (contract), first to pump blood into the ventricles. Then both ventricles contract to pump blood out of the heart into the arteries. There are one-way valves between the atria and ventricles and between the ventricles and the large arteries coming from the heart. The valves make sure that when the atria or ventricles contract, the blood flows in the correct direction.

Cross-section diagram of a normal heart

Cardiomyopathy means a disease of the heart muscle. There are four main types:

  • Dilated cardiomyopathy - where the heart enlarges (dilates).
  • Hypertrophic cardiomyopathy (HCM) - where the heart muscle becomes thickened (hypertrophied).
  • Restrictive cardiomyopathy - where the heart muscle cannot relax properly between heartbeats. This is rare.
  • Arrhythmogenic right ventricular cardiomyopathy - a rare type which mainly affects the right side of the heart.

In hypertrophic cardiomyopathy (HCM) the heart muscle becomes thickened (hypertrophies) in parts of the heart. In the normal heart, the muscle cells are regular and patterned. In HCM the cells of the heart muscle become irregular and disordered.

The muscle surrounding the left ventricle is the area commonly affected. Sometimes the muscle around the right ventricle is also affected. The degree of thickening may vary in different places. For example, the wall dividing the right and left ventricle (the septum) is often the area with the greatest thickening. In about 1 in 4 people the muscle thickening is evenly distributed throughout the walls of the left ventricle.

The thickened heart muscle usually squeezes (contracts) well to pump blood out of the heart. However, it may lead to problems which include the following:

  • The affected heart muscle (usually around the left ventricle) may become stiff. This can mean that your left ventricle may not fill as easily as normal. Less blood than normal is then pumped out from your heart with each heartbeat.
  • The thickening is often most marked in the upper part of the septum. This may partly obstruct the flow of blood from your left ventricle into your aorta. This results in less blood being pumped out from your heart. The partial obstruction may also make the blood flow turbulent. Turbulent blood flow can make small blood clots more likely.
  • The thickened heart muscle may affect the function of your heart valves. In particular, the mitral valve may become leaky if it does not close properly.
  • In some people, the abnormal heart muscle affects the electrical conducting system of the heart. This may cause abnormal heart rates and/or rhythms to develop.

Heart muscle can thicken because of something, such as high blood pressure. In HCM the heart muscle thickens without an obvious cause.

In most cases the condition is inherited. If a couple (where one person has HCM) has a child, there is a 1 in 2 chance of the child being affected. This pattern of inheritance is called autosomal dominant. It seems that affected people inherit defective genes which are involved in making parts of the heart muscle cells.

This condition affects about 1 in 500 people. It is sometimes present at birth and can develop in young children. However, it most commonly develops in early adulthood. HCM tends to affect men more often than women.

Most people with this condition do not have any symptoms. Symptoms can range from mild to severe and may not develop straightaway. Possible symptoms include the following:

  • Shortness of breath. This may develop only when you exercise if the condition is mild. When the condition is more severe, you can be breathless at rest.
  • Chest pain (angina). This may develop only when you exercise but it can also occur at rest when it is more severe. The pain occurs because the supply of blood and oxygen to the heart muscle is not sufficient to meet the demands of the thickened muscle.
  • Palpitations. Sometimes abnormalities of heart rhythm (arrhythmias) develop which can cause palpitations. You may become aware that your heartbeat is fast and/or irregular.
  • Dizziness and fainting attacks. These occur more commonly when you exercise but they may occur when you are resting. This may be due to reduced output of blood from the heart or because of arrhythmias.

The thickening of the heart muscle does not tend to progress once you stop growing. This means that, for many people, the symptoms remain stable during adulthood. Unfortunately, the symptoms gradually become worse for some people as the heart muscle becomes more stiff. Sometimes the function of the heart gradually deteriorates and heart failure may develop. See separate leaflet called Heart Failure.

A doctor may suspect this condition because of:

Once the diagnosis is confirmed, other tests may be needed to assess the severity of your condition. A Doppler ultrasound scan also looks at blood flow through the heart chambers. This shows how well the heart ventricles are filling and contracting. A Doppler ultrasound scan can also show if there is any turbulent blood flow within the ventricles.

Your first-degree relatives (mother, father, brother, sister, child) should have tests such as an ECG and an echocardiogram. Some people with HCM do not have any symptoms. This is why close relatives should be screened.

In some centres it may be possible to have a genetic blood test. The children of affected parents should be screened every three years until puberty, and then every year until they reach the age of 20 years.

There is no treatment which can reverse the changes of the heart muscle. Treatment aims to ease symptoms if they occur and to prevent complications. If you do not have any symptoms or you only have mild symptoms then you may not need any treatment.

Treatment which may be required includes the following:

General lifestyle advice


The medicines advised depend on what symptoms or complications develop. For example:

  • Beta-blockers (such as propranolol) and calcium antagonists (especially verapamil) are the commonly used medicines. These can slow the heart rate and make the heart squeeze (contract) less forcefully. This allows more time for the ventricle to fill with each heartbeat. These medicines may be used to treat chest pain, breathlessness and palpitations.
  • Various other medicines called anti-arrhythmic medicines (for example, amiodarone) are used to treat and to prevent abnormalities of heart rhythm (arrhythmias). They work by interfering with and helping to correct the electrical impulses in your heart.
  • An anticoagulant medicine may be advised if you develop atrial fibrillation (a common arrhythmia). With this arrhythmia a blood clot is a possible complication. Anticoagulant medicines help to prevent blood clotting by thinning the blood.

Other types of treatment for arrhythmias

Other treatments may be an option if you develop arrhythmias. For example:

  • Cardioversion is an option for some types of arrhythmia. Whilst under anaesthetic, you are given an electric shock over the heart. This may revert the rhythm back to normal.
  • Artificial pacemakers are used in certain types of arrhythmia where the heart beats abnormally slowly (complete heart block) and in certain other situations. An artificial pacemaker is a small device which is inserted just under the skin on the upper chest. Wires from the pacemaker are passed through veins into the heart chambers. The pacemaker can then stimulate the heart to maintain a regular normal heartbeat.
  • Implantable cardioverter defibrillators (ICDs) are sometimes used in certain situations - especially if you are at risk of developing serious and life-threatening arrhythmias. They are small devices which are similar to pacemakers and are inserted under the skin in the upper chest. Wires are passed through a vein to the heart. The device monitors the heartbeat. If it detects an abnormal rhythm, the device can send a small electrical shock to the heart to change it back to normal.


If your cardiomyopathy is severe, an operation may be an option:

  • Myectomy. This is an operation to remove a segment of thickened muscle from the wall dividing the right and left ventricle (the septum). It is done as open heart surgery. It is not a cure but it can help when the thick septum is causing obstruction to the flow of blood through the aortic valve.
  • Alcohol septal ablation. Alcohol is injected into the small blood vessels (arteries) which supply the thickened area of heart muscle. This destroys that part of muscle, which then becomes thinner.
  • Valve replacement may be needed if the mitral valve is affected and does not work properly.
  • A heart transplant may be needed in a very small number of people.

The severity of HCM and the complications caused by HCM vary from person to person. The possible complications include:


An arrhythmia is an abnormal rate or rhythm of the heartbeat. There are various types of arrhythmia, some more serious than others. Sometimes an arrhythmia develops intermittently and can cause bouts of palpitations, dizziness and other symptoms. Some arrhythmias become permanent. Arrhythmias can usually be treated. See separate leaflet called  Abnormal Heart Rhythms (Arrhythmias).


This is a rare complication. Endocarditis is an infection of the inside lining of the heart chambers and heart valves. Unless promptly treated, endocarditis can cause serious illness.

People with HCM used to be advised to take antibiotic medicines before dental treatment or other procedures. This is no longer the case, as taking antibiotics has not been shown to reduce the risk of developing infective endocarditis. See separate leaflet called Infective Endocarditis.

Sudden death

Sudden collapse and death occurs in a small number of people with HCM. This is probably due to a severe arrhythmia which may develop suddenly. Some people at high risk may be advised on treatments which aim to prevent or treat arrhythmias.

The thickening of the heart muscle does not tend to progress once you stop growing. This means that, for many people, the symptoms remain stable during adulthood. Unfortunately, the symptoms gradually become worse for some people as the heart muscle becomes more stiff. Sometimes the function of the heart gradually deteriorates and heart failure may develop. See separate leaflet called Heart Failure for more details.

Further reading and references

  • ; NICE Clinical Guideline (March 2008)

  • ; Diagnosis and management of hypertrophic cardiomyopathy. Echo Res Pract. 2015 Mar 12(1):R45-53. doi: 10.1530/ERP-15-0007. Epub 2015 Mar 11.

  • ; Advances in medical treatment of hypertrophic cardiomyopathy. J Cardiol. 2014 Apr 12. pii: S0914-5087(14)00077-X. doi: 10.1016/j.jjcc.2014.02.022.

  • ; Hypertrophic cardiomyopathy. Lancet. 2013 Jan 19381(9862):242-55. doi: 10.1016/S0140-6736(12)60397-3. Epub 2012 Aug 6.

  • ; Atrial fibrillation and thromboembolism in patients with hypertrophic cardiomyopathy: systematic review. Heart. 2014 Mar100(6):465-72. doi: 10.1136/heartjnl-2013-304276. Epub 2013 Sep 7.

This is making me ridiculously anxious... few months back i wass having palpitations where i noticed my hearr rate was fairly slow 58/59 at rest i was worried went doctors had an ecg - nothibg showed...

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