• Hypertrophic cardiomyopathy (HCM) causes the heart muscle to thicken, preventing the heart from pumping blood efficiently.
• HCM is an inherited disease that runs in families.
• People with HCM may not have any symptoms, or they may only have symptoms during or after vigorous physical activity.

Cardiomyopathies are diseases that occur in the heart muscle. One of the most common types of cardiomyopathy is hypertrophic cardiomyopathy. HCM is a genetic disease that causes the heart muscle to thicken and harden, which weakens the heart.

What Is Hypertrophic Cardiomyopathy?

HCM causes the walls of the heart’s left ventricle — one of the four chambers of the heart — to grow thicker (hypertrophy) and become stiff, making it more difficult for the heart to pump blood.

When the walls of the heart grow thick, they can become less flexible and make the inside of the left ventricle smaller and stiffer. This prevents the left ventricle from properly filling with blood and efficiently pumping oxygen-rich blood to the body. Thickening of the left ventricle can interfere with heart valve function and may obstruct blood flow from the heart to the body.

HCM can progress and lead to heart failure and other complications, including:

• Arrhythmia (irregular heartbeat or abnormal heart rhythms)
• Heart failure
• Stroke
• Cardiac arrest

HCM can begin during childhood, but may not cause problems until much later in life.

Detecting HCM early in the disease’s progression can be difficult. It can also be hard to diagnose in people who are athletic. Exercise can strengthen the heart and make the left ventricle grow larger, which can mask the early stages of HCM.

HCM affects approximately 1 in 500 people in the United States. It runs in families and is the most common inherited heart condition.

What Are the Symptoms of Hypertrophic Cardiomyopathy?

Many people with HCM do not have any symptoms at all. When people do have symptoms, they may only occur during or after exercise or vigorous activity. If symptoms occur at rest, it may indicate more advanced disease.

Symptoms of HCM can include:

• Chest pain
• Shortness of breath
• Fatigue
• Dizziness or lightheadedness
• Syncope (fainting)
• Palpitations, faster heart rate, or a fluttering sensation in the chest
• Irregular heartbeat
• Cardiac arrest

People with HCM may have one or more of these symptoms or none at all. None of the symptoms of HCM are unique, and they can all occur with many other health conditions. If you have problems with breathing or heart symptoms, take them seriously and discuss them with your doctor.

What Causes Hypertrophic Cardiomyopathy?

HCM is an inherited disease caused by gene mutations (changes in genes). Several genes have been identified that have mutations associated with HCM, including:

• MYH7
• MYBPC3
• TNNT2
• TNNI3

Each of these genes has a different function, but they are all involved in creating the proteins that make up the heart muscle.

Scientists believe that gene mutations associated with HCM cause abnormalities in the structure and function of heart tissue. Normally, heart muscle tissue grows in an orderly way, but in people with HCM, heart muscle fibers grow in a disorganized pattern.

Ultimately, this leads to the heart muscle growing thicker and stiffer, preventing the heart from relaxing and filling with blood as it should. HCM arrhythmias, such as atrial fibrillation (AFib), are irregular heart rhythms caused by abnormal electrical conduction through damaged heart muscle. Arrhythmias can sometimes lead to life-threatening complications, including blood clots, stroke, and cardiac arrest.

Along with left ventricular abnormalities, HCM can also affect the septum (wall) between the left and right ventricles. A thickened septum can obstruct blood flow into the aorta, the large artery that carries blood from the heart to the rest of the body. This is called obstructive hypertrophic cardiomyopathy.

Could You Have Hypertrophic Cardiomyopathy?

HCM is inherited in an autosomal dominant pattern. This means that you only need to inherit one copy of a mutated gene from one parent in order to develop the disease. A person with HCM has a 50 percent chance of passing this gene on to their child.

If you have a close family member with HCM, such as a parent, grandparent, or sibling, then you are at greater risk of having HCM. However, HCM may go undiagnosed in many people with a higher risk who do not have obvious symptoms of the condition.

Even for someone who does have symptoms, diagnosing HCM can be difficult because symptoms of the condition are also seen in other medical conditions. Diagnosing HCM involves a thorough medical history and physical exam followed by imaging and laboratory tests such as echocardiogram, cardiac MRI, and genetic testing. A careful and accurate diagnosis of HCM is extremely important for determining the appropriate HCM treatment.

Sudden Cardiac Death

Some people with HCM may have a higher risk of sudden cardiac death (SCD, also called sudden cardiac arrest), though this is rare. Sudden cardiac death can also occur in people with undiagnosed HCM who have never had any symptoms.

If you know you’re at higher risk of having HCM or if you have a family history of SCD, talk to your doctor before participating in vigorous physical activity, such as football, basketball, soccer, or running. SCD mostly affects older people, but it can occur in young people participating in athletics. Sometimes, implantable cardioverter defibrillators (ICDs) are recommended to protect you from SCD.

Knowing the symptoms of HCM — and, more importantly, understanding your risk of developing the condition — can help you avoid serious complications of HCM. If you think you may be at risk of HCM, be sure to get medical advice before dangerous health issues arise.

Talk With Others Who Understand

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