• Hypertrophic cardiomyopathy (HCM) causes the heart muscle to thicken, preventing the heart from pumping blood to the body 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), a genetic disease that makes the heart muscle thicken and harden too much to function properly.

What Is Hypertrophic Cardiomyopathy?

HCM is a disease of the heart muscle (cardiomyopathy) that causes the walls of the heart’s left ventricle 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, preventing it from filling with blood as it should. If the left ventricle cannot fill properly, it cannot pump oxygen-rich blood to the body efficiently. Thickening of portions of the left ventricle can interfere with heart valve function and may obstruct blood flow from leaving the heart.

HCM may be a progressive disease that can lead to heart failure and other complications, including irregular heartbeat (arrhythmia), heart failure, stroke, and cardiac arrest. Changes in the heart caused by HCM can begin during childhood, but they may not cause problems until much later in life.

It can be difficult to detect heart changes due to HCM early in the disease and in people who are athletic. Exercise can strengthen the heart and make the left ventricle grow larger, which can be difficult to distinguish from 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
• Fainting (also called syncope)
• Palpitations, faster heartbeat, or a fluttering sensation in the chest
• Irregular heartbeat

People with HCM may have one or more of these symptoms or none at all. None of the symptoms of HCM are unique. Many conditions can cause some or all of these same symptoms. If you have problems with breathing and heart symptoms, take them seriously and discuss them with your doctor.

What Causes Hypertrophic Cardiomyopathy?

HCM is an inherited disease caused by gene mutations. Several genes have been identified that have mutations associated with HCM, including MYH7, MYBPC3, TNNT2, and TNNI3. Each of these genes has a different function, but they are all involved in creating the proteins that make up heart muscle.

Mutations in these genes lead to abnormalities in the normal structure and function of heart tissue. Normally, heart muscle grows in an orderly and organized way, but in 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. It can also cause arrhythmias — irregular heart rhythms caused by abnormal conduction of electrical impulses through the heart muscle. Arrhythmias can sometimes lead to life-threatening complications, including blood clots, stroke, and cardiac arrest.

HCM affects the walls of the left ventricle and usually also involves the septum (wall) between the left and right ventricles. When the septum becomes thickened, it can cause obstruction of blood flow into the aorta, the large artery that carries blood from the heart to the rest of the body. This is called obstructive HCM.

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 relative with HCM, such as a parent, grandparent, or sibling, you are at greater risk of having HCM. However, HCM may go undiagnosed in many people who do not have symptoms, so you may not know if you have a higher risk.

Even when a person does have symptoms, HCM can be difficult to diagnose because many features 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. A careful and correct diagnosis of HCM is extremely important for determining the appropriate treatment.

Sudden Cardiac Death

Certain people with HCM may be at higher risk of sudden cardiac death, also called SCD or sudden cardiac arrest, but it is rare. SCD can also occur in people with undiagnosed HCM who have never had any symptoms.

If you know you are at higher risk of having HCM or if you have a family history of SCD, discuss your risk with a 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.

Knowing the symptoms of HCM and, perhaps more importantly, understanding your risk of disease can help you avoid serious complications by seeking medical advice before dangerous health issues arise.

Talk With Others Who Understand

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