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What causes a weak heart muscle?

A weak heart muscle, known medically as cardiomyopathy, is a condition where the heart muscle becomes enlarged, thick, or rigid. This affects the heart’s ability to pump blood effectively. A weak heart muscle can be caused by a variety of factors.

What is cardiomyopathy?

Cardiomyopathy refers to diseases of the heart muscle that affect its size, shape, and structure. This impacts the heart’s ability to pump blood effectively. The main types of cardiomyopathy are:

  • Dilated cardiomyopathy – heart muscle becomes enlarged and weakened
  • Hypertrophic cardiomyopathy – heart muscle thickens
  • Restrictive cardiomyopathy – heart muscle becomes rigid and less elastic

In dilated cardiomyopathy, the left ventricle stretches and becomes thinner, so it can’t pump blood as well as a healthy heart. This is the most common type.

With hypertrophic cardiomyopathy, the heart muscle cells enlarge and cause the walls of the ventricles to thicken. This makes the ventricles stiff, reducing the amount of blood they can hold.

In restrictive cardiomyopathy, the heart muscle becomes rigid and less elastic. This restricts the heart’s ability to fill with blood between beats.

What causes a weak heart muscle?

There are various causes of a weak heart muscle, including:

Dilated cardiomyopathy

  • Viral infections – viruses like HIV, herpes, and hepatitis C can damage heart muscle
  • Toxins – alcohol, cocaine, some chemotherapy drugs
  • Metabolic disorders – thyroid problems, diabetes
  • Nutritional deficiencies – thiamine, selenium, protein
  • Autoimmune disorders – immune system attacks heart muscle
  • Pregnancy complications
  • Genetic mutations – can alter proteins in heart muscle cells

Hypertrophic cardiomyopathy

  • Genetic mutations – in genes affecting heart muscle proteins
  • High blood pressure
  • Aging

Restrictive cardiomyopathy

  • Radiation therapy
  • Chemotherapy
  • Metabolic disorders like amyloidosis
  • Hemochromatosis – too much iron in body
  • Sarcoidosis – inflammatory cells form clusters in organs

In many cases, the exact cause is unknown. Sometimes cardiomyopathy develops as a result of another underlying condition like coronary artery disease or hypertension. A combination of factors is often responsible.

Risk factors

Certain factors can increase your risk of developing a weak heart muscle:

  • Genetics – family history of cardiomyopathy
  • Viral infections
  • High blood pressure
  • Diabetes
  • Obesity
  • Excessive alcohol use
  • Smoking
  • Age – more common in adults over 60
  • Gender – more common in men
  • Lifestyle factors like lack of exercise, poor diet, stress


Signs and symptoms of cardiomyopathy and weak heart muscle include:

  • Shortness of breath, especially with activity or when lying down
  • Fatigue and weakness
  • Swelling in legs, ankles and feet
  • Dizziness, lightheadedness
  • Heart palpitations
  • Chest pain
  • Fainting or passing out

Severe cardiomyopathy can lead to complications like heart failure, blood clots, or irregular heartbeats (arrhythmias). Symptoms may develop gradually or come on suddenly.


If cardiomyopathy is suspected, diagnostic tests may include:

  • Medical history and physical exam
  • Blood tests
  • Chest x-ray
  • Electrocardiogram (ECG)
  • Echocardiogram – uses ultrasound to visualize heart
  • Cardiac MRI
  • Stress test
  • Cardiac catheterization – check heart arteries
  • Genetic testing

These tests help identify any structural changes in the heart muscle and determine the type of cardiomyopathy present.


Treatment options for cardiomyopathy depend on the cause and type. They aim to manage symptoms and prevent complications. Treatments may include:

  • Treating underlying conditions like viral infections, thyroid disorders
  • Lifestyle changes – healthy diet, exercise, stress management, avoiding toxins like alcohol and cocaine
  • Medications – ACE inhibitors, beta blockers, diuretics, blood thinners
  • Implantable devices – pacemaker, defibrillator, ventricular assist device
  • Surgery – septal myectomy for hypertrophic cardiomyopathy, heart transplant if severe

Treatment can help improve quality of life and slow the progression of cardiomyopathy. But the damage to the heart muscle is often irreversible.


Steps that may help prevent cardiomyopathy include:

  • Manage health conditions like high blood pressure, diabetes, thyroid disorders
  • Get vaccines to protect against viruses that can damage the heart
  • Avoid toxins like cocaine, excess alcohol
  • Maintain healthy diet and weight
  • Don’t smoke
  • Reduce stress
  • Exercise regularly
  • Limit caffeine
  • Get health screenings as recommended

While cardiomyopathy is not always preventable, leading a healthy lifestyle provides the best chance to lower risk.

Outlook and prognosis

The prognosis for cardiomyopathy varies depending on the cause and severity of damage to the heart. Mild cases may have minimal impact on longevity. Advanced cardiomyopathy can lead to severe heart failure and death.

With treatment, some people with cardiomyopathy can manage symptoms for decades. But over time, the condition may worsen. Getting care early provides the best outlook.

Key points

  • Cardiomyopathy refers to diseases affecting the heart muscle that make it difficult to pump blood.
  • Main types are dilated, hypertrophic, and restrictive cardiomyopathy.
  • Causes include genetics, viral infections, toxins, metabolic disorders, autoimmune diseases.
  • Symptoms include shortness of breath, swelling, fatigue, palpitations.
  • Risk factors include genetics, hypertension, obesity, diabetes, lifestyle factors.
  • Treatment focuses on managing symptoms and complications.
  • Leading a healthy lifestyle may help prevent some forms of cardiomyopathy.
  • Prognosis varies greatly depending on cause and severity.


Cardiomyopathy, or a weak heart muscle, has a range of causes. Genetics, viral infections, toxins, chronic conditions like diabetes, and lifestyle factors can all contribute to structural changes in the heart muscle. These changes affect the heart’s ability to pump blood effectively. Symptoms of cardiomyopathy include shortness of breath, swelling, fatigue and heart palpitations. Diagnostic tests like echocardiograms and cardiac MRIs identify the type of cardiomyopathy present. While treatment can help manage the condition, damage to the heart muscle is often irreversible. Leading a healthy lifestyle is the most effective way to lower risk of developing cardiomyopathy. The prognosis varies greatly depending on the severity of the weak heart muscle.