Dilated cardiomyopathy is a condition where the heart’s main pumping chamber stretches and weakens, making it harder for the heart to push blood through the body. This disease affects the structure of the heart muscle itself, causing the chambers to grow larger and the walls to become thinner over time, which reduces the heart’s ability to function properly.

Understanding How Common This Condition Is

Dilated cardiomyopathy affects approximately 36 people per 100,000 in the general population, according to research estimates. This makes it one of the more significant heart muscle diseases that doctors encounter in their practice.^[1] The condition does not affect everyone equally. It is more common in men than in women, and appears about twice as often in people of African ancestry compared with White people.^[1][2]

The disease can develop at any age, but most commonly appears in adults younger than 50 years old. About 10% of people who develop dilated cardiomyopathy are older than 65.^[3] In children, cardiomyopathies are less common, with an estimated incidence of about 1 case per 100,000 person-years, and roughly 50% of these childhood cases are classified as dilated cardiomyopathy.^[4]

The rate at which people develop this condition is approximately 5 to 6 individuals per 100,000 each year. The United States sees the disorder occur in three times as many males as females.^[5] Dilated cardiomyopathy represents a common cause of heart failure and is frequently the reason why patients need heart transplants.^[6]

What Causes the Heart Muscle to Weaken

In many cases, doctors cannot identify a specific cause for dilated cardiomyopathy. When no clear reason can be found, the condition is called idiopathic dilated cardiomyopathy, which simply means the origin is unknown.^[1] This lack of an identifiable cause happens frequently, and the diagnosis is made only after doctors have ruled out all other possible secondary causes.

When a cause can be identified, it falls into several categories. The most common known causes include heart disease resulting from narrowed or blocked coronary arteries and poorly controlled high blood pressure.^[2] However, it is important to understand that when coronary artery disease is the primary problem, doctors typically classify this as a separate condition called ischemic cardiomyopathy rather than dilated cardiomyopathy.

Genetics play a major role in many cases. Familial dilated cardiomyopathy, which is the form passed down through families, may account for more than 50% of all cases.^[3] The condition has been linked to changes in genes that affect different parts of heart cells, including proteins in the cytoskeleton, nuclear membrane, and contractile structures. Mutations in genes for Desmin, Lamin C, or Myosin have been associated with the disease.^[4]

Infections can trigger the condition. Viral infections are believed to be responsible for many cases, with more than 20 different viruses capable of causing dilated cardiomyopathy. In temperate regions, coxsackievirus B is the most common viral culprit. Other infections include Chagas disease caused by the parasite Trypanosoma cruzi, which is the most common infectious cause in Central and South America, as well as HIV, toxoplasmosis, and Lyme disease.^[5]

Toxic substances can damage the heart muscle. Prolonged heavy use of alcohol is a well-known cause, as are certain illegal drugs like cocaine. Various organic solvents, heavy metals such as lead, arsenic, cobalt, or mercury, and specific chemotherapy drugs used to treat cancer, including doxorubicin and trastuzumab, can be toxic to the heart.^[6]

Other medical conditions can lead to dilated cardiomyopathy. These include diabetes, thyroid disease, viral hepatitis, autoimmune illnesses, and conditions that affect the heart valves. Abnormal heart rhythms, particularly when the heart beats very fast for prolonged periods, can also cause the condition. Frequent ventricular ectopy, with more than 10,000 extra beats from the ventricles each day, has been linked to problems with the left ventricle’s pumping function.^[7]

Pregnancy-related causes include complications during the late stages of pregnancy or within five months after childbirth, a condition known as peripartum cardiomyopathy.^[8] Some individuals have multiple contributing factors. For example, a person might have a genetic predisposition and then develop a medical condition that triggers the full disease.

Who Is More Likely to Develop This Condition

Several factors increase the likelihood of developing dilated cardiomyopathy. Age plays a role, with people younger than 50 being more commonly affected. Being male increases risk, as the condition occurs more frequently in men than women across all populations.^[1]

Race and ethnicity matter. People of African or Black ancestry face higher risk, with the condition appearing about twice as often compared to White individuals. Troublingly, the risk of dilated cardiomyopathy progressing to severe illness and heart failure is higher in Black patients than White patients, even when controlling for other medical conditions and socioeconomic factors.^[2]

Family history is one of the most significant risk factors. If you have biological relatives with dilated cardiomyopathy, your risk increases substantially. More than 50 genes related to the condition have been identified, and genetic forms may account for up to half of all cases.^[3] This is why doctors often recommend that first-degree relatives of someone with dilated cardiomyopathy undergo screening, even if they have no symptoms.

How the Disease Affects Your Daily Life

Many people with dilated cardiomyopathy experience no symptoms at all, especially in the early stages of the disease. The condition can develop slowly and quietly, which means some individuals might not realize anything is wrong until the heart has already weakened considerably.^[1] This silent progression makes regular check-ups important for people at risk.

As the disease advances and heart function declines, symptoms begin to appear and typically worsen over time. Fatigue, or feeling unusually tired and weak, is one of the most common complaints. This happens because the heart cannot pump enough blood to meet the body’s needs, leaving you feeling drained of energy even during routine activities.^[2]

Shortness of breath, medically called dyspnea, becomes noticeable during physical activity or even while lying down. You might find yourself getting winded when climbing stairs, walking short distances, or trying to sleep flat in bed. Some people wake up at night gasping for air because fluid builds up in the lungs when lying horizontal.^[3]

Swelling, known as edema, often develops in the legs, ankles, and feet. Your belly, called the abdomen in medical terms, may also swell. This swelling happens because the weakened heart cannot move blood efficiently through the circulatory system, causing fluid to accumulate in tissues. You might notice your shoes feel tight by the end of the day, or see indentations in your skin where socks or shoe straps pressed.^[4]

Unexpected weight gain can occur rapidly due to fluid retention. If you suddenly gain 1 to 1.3 kilograms (2 to 3 pounds) in a day or 2.3 kilograms (5 pounds) in a week, this could signal that your condition is worsening.^[5] Keeping track of your weight daily helps catch these changes early.

Chest discomfort or pain may occur, though this is not always present. Some people experience palpitations, which feel like your heart is racing, fluttering, or pounding unusually hard in your chest. These sensations happen when the heart develops abnormal rhythms as it struggles to function properly.^[6]

Dizziness, lightheadedness, and fainting can happen when the heart cannot maintain adequate blood flow to the brain. A reduced ability to exercise or perform physical tasks that were once easy becomes apparent. You might notice you cannot walk as far, carry as much, or keep up with activities you used to enjoy.^[7]

Coughing and congestion may develop as fluid accumulates in the lungs. This cough can be persistent and might produce pink, foamy mucus in severe cases, indicating significant heart failure.^[8]

Steps to Reduce Your Risk

While you cannot change genetic factors or prevent all causes of dilated cardiomyopathy, there are important steps you can take to reduce your risk or slow the disease if you already have it. A heart-healthy lifestyle forms the foundation of prevention and disease management.

If you smoke, quitting is one of the most important actions you can take. Smoking makes any heart condition worse and directly damages blood vessels and heart tissue. Many programs and medications exist to help people quit successfully, so talk with your doctor about options that might work for you.^[1]

Limiting or eliminating alcohol consumption matters significantly. Prolonged heavy alcohol use is a recognized cause of dilated cardiomyopathy, and even moderate drinking might worsen existing heart muscle disease. If you drink alcohol, discuss safe limits with your healthcare provider, or consider stopping entirely.^[2]

Avoiding illegal drugs, especially cocaine and other substances toxic to the heart, protects your heart muscle from damage. These substances can cause immediate and long-term harm to the cardiovascular system.^[3]

Managing other health conditions helps prevent secondary causes of dilated cardiomyopathy. Keep diabetes under control through proper diet, exercise, and medications as prescribed. Monitor and treat high blood pressure consistently, as uncontrolled hypertension can lead to heart muscle damage over time. Work with your doctor to manage high cholesterol and thyroid disease.^[4]

If you receive chemotherapy for cancer treatment, your doctors should monitor your heart function carefully. Some cancer drugs are known to be cardiotoxic, meaning they can harm the heart. Early detection of heart problems during cancer treatment allows for adjustments to protect your heart while still fighting cancer.^[5]

For people with a family history of dilated cardiomyopathy, regular screening is crucial. First-degree relatives, including parents, siblings, and children of someone with the condition, should undergo periodic evaluation even without symptoms. This screening typically includes a clinical examination, an electrocardiogram or EKG to check the heart’s electrical activity, and an echocardiogram or ultrasound to look at heart structure and function. Genetic testing might be offered to identify disease-causing mutations.^[6]

Getting vaccinated protects you from infections that could worsen heart function. Vaccines against COVID-19, influenza, and pneumonia are particularly important for people with heart conditions or those at risk.^[7]

Changes That Happen Inside Your Heart

Understanding what happens to the heart muscle in dilated cardiomyopathy helps explain why symptoms develop and why treatment is necessary. The disease represents a primary disorder of the heart muscle itself, meaning something is fundamentally wrong with the muscle tissue rather than being caused by blocked arteries or valve problems.

The process typically begins in the heart’s main pumping chamber, called the left ventricle. This muscular chamber normally contracts forcefully to push oxygen-rich blood out to the entire body. In dilated cardiomyopathy, the walls of the left ventricle experience increased stress and begin to stretch out. As the tissue stretches, it also becomes thinner, much like how a balloon’s surface becomes thinner as you inflate it.^[1]

This stretching and thinning causes the left ventricle to grow larger, or dilate, which is where the condition gets its name. The enlarged, thinned muscle cannot contract as strongly as it should. Each time the heart beats, it fails to pump out as much blood as a healthy heart would. More blood remains in the chamber after each heartbeat, which causes even more stretching and weakening in a downward spiral.^[2]

The heart muscle’s pumping strength is measured by something called ejection fraction, abbreviated as EF. This number represents the percentage of blood that leaves the ventricle with each beat. A normal ejection fraction is about 60%, meaning 60% of the blood in the left ventricle is pushed out with each contraction. In dilated cardiomyopathy, the ejection fraction drops below 40%, indicating significant pumping problems.^[3]

As the left ventricle dilates, it affects other parts of the heart. The muscle may try to compensate by growing thicker in some areas, a process called hypertrophy. However, this compensatory thickening is not enough to maintain normal function. The enlargement often spreads beyond the left ventricle. In severe cases, the right ventricle and both of the heart’s upper chambers, called atria, also become enlarged.^[4]

The valves inside your heart, which normally act as one-way doors to keep blood flowing in the correct direction, can malfunction as the chambers stretch. The mitral valve between the left atrium and left ventricle, and the tricuspid valve between the right atrium and right ventricle, may fail to close completely. This allows blood to leak backward, a problem called regurgitation, which further reduces the heart’s efficiency.^[5]

When blood does not move efficiently through the heart, it can pool in the enlarged chambers. This stagnant blood increases the risk of blood clots forming inside the heart. These clots are dangerous because they can break free and travel through the bloodstream. A clot that reaches the lungs causes a pulmonary embolism, while a clot reaching the brain causes a stroke. Both are life-threatening emergencies.^[6]

The electrical system of the heart, which normally coordinates the heart’s rhythmic beating, often becomes disrupted in dilated cardiomyopathy. Abnormal heart rhythms, called arrhythmias, are common. These can include dangerously fast rhythms from the ventricles or irregular rhythms like atrial fibrillation from the stretched atria. Some people develop problems with the electrical signals that travel between the upper and lower chambers, called atrioventricular block.^[7]

The weakened, enlarged heart struggles increasingly to meet the body’s demands for blood flow. As the muscle continues to deteriorate, the reduced pumping ability leads to a condition called heart failure. This does not mean the heart stops completely, but rather that it fails to pump adequately. Heart failure explains why symptoms like fatigue, shortness of breath, and swelling develop and worsen over time. Without treatment, dilated cardiomyopathy is progressive, meaning it continues to get worse, leading to severe heart failure, dangerous arrhythmias, and potentially death.^[8]