Hypertrophic cardiomyopathy (HCM) is a genetic condition characterized by the thickening of the heart muscles.

This can happen at any time in life but often begins in adolescence or early adulthood. Because symptoms may be mild or unnoticeable, many people do not receive a diagnosis until later in adulthood.

Review the graphic below to learn more about the ways HCM can affect the structure and rhythms of the heart.

There are two types of HCM:

  • obstructive
  • nonobstructive

In both forms of HCM, the muscles of the left ventricle are thickened.

In obstructive HCM, the enlarged muscles block or reduce the flow of blood out of the left ventricle and into the aorta. This means the heart has to work harder to pump blood to the rest of the body.

It can cause symptoms like exercise intolerance and lightheadedness. Obstructive HCM may also cause changes in blood flow that may result in a heart murmur. A doctor can hear this murmur during a regular physical examination.

Obstructive HCM is the most common type, accounting for about 75% of cases of HCM.

The signs and symptoms of HCM can vary widely from person to person, even within the same family. Many people do not experience any symptoms at first. As the disease progresses, however, a variety of symptoms can happen.

According to the American Heart Association (AHA), these symptoms may include:

  • shortness of breath, especially with activity or when lying flat
  • chest pain with activity
  • fainting, lightheadedness, or dizziness
  • fluttering or pounding heartbeats, known as palpitations
  • excessive tiredness
  • swelling in the abdomen, legs, ankles, or feet (peripheral edema)
  • atypical heart rhythms

Not all people experience symptoms at first, or they may be very mild. Over time, however, symptoms may appear or become more severe.

HCM is not considered a form of heart failure, but it can increase the likelihood that heart failure will develop.

Heart failure occurs when the heart cannot pump blood as efficiently as it should. Heart failure is a chronic, progressive condition, in which the heart attempts to make up for the less efficient pumping by doing one or more of the following:

  • getting larger
  • developing more muscle mass
  • pumping faster

A person may not realize they are experiencing heart failure because the heart — and body — have temporarily masked the condition. Eventually, a person will start to experience symptoms like fatigue or shortness of breath that prompt them to visit their doctor.

Severe heart failure affects about 10% to 20% of people with HCM. Those most likely to be affected by heart failure include:

  • older adults
  • people with obstructive HCM
  • people who also have arrhythmias, such as atrial fibrillation (AFib)

In rare cases, heart failure in HCM may require heart transplantation. It is important for people with HCM to be regularly monitored by a cardiologist to help prevent severe complications from their condition.

HCM is a progressive disease, meaning the symptoms can get worse over time. As the disease progresses, it can also lead to other health complications, such as:

  • arrhythmias, like atrial fibrillation
  • blood clots and stroke
  • heart failure
  • sudden cardiac arrest, in rare cases

Treatment of HCM is aimed at managing the symptoms of the condition as well as preventing potential complications.

In general, HCM is a chronic health condition that can worsen over time. Most people with HCM have a typical life expectancy, without significant limitations to their daily activities or severe complications. This is true regardless of whether they have obstructive or nonobstructive HCM, the AHA says.

To reduce the risk of complications, a healthcare professional may prescribe medications to help manage symptoms, arrhythmias, and heart failure. In serious cases, surgical and nonsurgical procedures may be used to help restore blood flow in the heart.

These may include:

  • septal myectomy (an open-heart surgery in which the muscle of the septum blocking the flow of blood is removed)
  • nonsurgical septal ablation
  • implantation of an electronic heart device (e.g., implantable cardioverter-defibrillator)
  • heart transplant

A heart-healthy lifestyle can also help reduce the risk of complications, including staying active, eating a heart-healthy diet, and avoiding smoking. Sometimes high intensity physical activity needs to be avoided. A person should discuss participation in sports and exercise with a cardiologist, the AHA advises.