Myocarditis is an inflammatory condition affecting the heart muscle that can strike without warning, reducing the heart’s ability to pump blood effectively and causing symptoms ranging from mild chest discomfort to severe heart failure.

Understanding Myocarditis: A Global Health Concern

Myocarditis represents a relatively rare but important heart condition that affects people worldwide. According to current estimates, approximately 1.3 million cases of myocarditis were diagnosed globally in 2021, with researchers calculating that around 10 to 20 people out of every 100,000 are affected each year^[2][4]. This means that roughly 1.5 million cases occur worldwide annually, making it a condition that, while uncommon, touches thousands of lives across different continents and communities^[4].

The disease does not affect everyone equally. Young adults appear to be at higher risk, though people of all ages can develop myocarditis^[4]. Men are more frequently affected than women, though females certainly can and do develop the condition^[4]. Because many individuals and even some physicians are unfamiliar with this condition, diagnosis can be challenging, and awareness remains limited despite the significant number of people affected each year^[2].

What Causes Myocarditis?

The causes of myocarditis are diverse, ranging from infectious agents to autoimmune reactions and medication side effects. Understanding what triggers this inflammation of the heart muscle is essential for both prevention and treatment. Viral infections stand out as the leading cause of myocarditis^[2]. The inflammation occurs during the course of infection, placing stress on the heart that can persist even after the initial infection has resolved^[2].

Many different viruses have been linked to myocarditis. Common culprits include the influenza virus, adenovirus (a virus that typically causes cold-like symptoms), coxsackie virus (a common virus that can cause various illnesses), parvovirus B19 (which can cause a distinctive facial rash in children), and herpes virus six^[4][17]. More recently, SARS-CoV-2, the virus responsible for COVID-19, has been identified as a cause of myocarditis^[4]. Interestingly, many people develop myocarditis without having experienced typical viral symptoms like cough, nasal congestion, or rash beforehand, only becoming aware of the infection when heart-related symptoms appear^[17].

Beyond viral infections, bacterial infections can also trigger myocarditis, though this occurs less frequently. Rarely, myocarditis develops as a complication of endocarditis, which is an infection affecting the heart valves and the inner lining of the heart’s chambers^[17]. Chagas disease, caused by a parasite transmitted through insect bites and most common in Central and South America, represents another infectious cause that can lead to chronic myocarditis developing years after the initial infection^[17].

Cancer, fungal infections, and other contagious diseases can also lead to myocarditis^[2]. Environmental toxins ranging from metal poisons to spider and snake venom have been documented as causes^[2]. Exposure to radiation or heavy metals can trigger the condition as well^[4].

A particularly concerning cause involves autoimmune disorders, where the body’s immune system mistakenly attacks its own tissues. Conditions such as systemic lupus erythematosus (commonly called lupus), rheumatoid arthritis, and sarcoidosis can all lead to myocarditis^[4][17]. A small group of individuals with autoimmune conditions may develop giant cell myocarditis, a variation of the disease that often results in rapid deterioration but may still respond successfully to treatment, especially when diagnosed early^[2].

The Connection Between COVID-19 Vaccines and Myocarditis

In rare cases, myocarditis has occurred in young people who received certain COVID-19 vaccines, specifically the Pfizer-BioNTech or Moderna vaccines^[4]. Symptoms can begin during the first week after receiving the vaccine^[4]. Several recent studies indicate that both the COVID-19 virus itself and the vaccines may cause myocarditis, with an estimated three in every 1,000 patients hospitalized due to COVID-19 infection potentially at risk for developing acute myocarditis^[16].

Most people who experience this reaction to the COVID-19 vaccine recover quickly after treatment and can return to their regular activities when they feel better^[4]. However, anyone who has had myocarditis should check with a cardiologist before starting to exercise again^[4]. The Centers for Disease Control and Prevention continues to recommend the vaccine, noting that the risk from COVID-19 itself is higher than the small risk of these rare side effects^[4].

Risk Factors: Who Is More Vulnerable?

Certain characteristics and circumstances increase the likelihood of developing myocarditis. Some of these risk factors cannot be changed, while others relate to lifestyle choices or medical treatments. Genetics play a subtle but important role in myocarditis risk. Between 6% and 18% of myocarditis patients carry a genetic mutation associated with increased risk of cardiomyopathy, which is a disease of the heart muscle^[2]. While you don’t inherit myocarditis directly, your genes influence how your body handles inflammation and how likely you are to develop the condition^[4].

Age and gender also matter. Young adults face higher risk, though people of all ages can develop myocarditis^[4]. Males are more susceptible than females, though women certainly can develop the condition as well^[4]. Consuming more alcohol than the limit your healthcare provider recommends increases your risk^[4].

Medical treatments and procedures can elevate myocarditis risk. These include dialysis treatment, having implanted heart devices, radiation therapy, treatments for heart problems, and having a central venous line (a catheter placed in a large vein for medication or fluid administration)^[4]. People whose bodies don’t react well to inflammation face increased vulnerability^[4].

Recognizing the Symptoms

One of the greatest challenges in diagnosing and treating myocarditis is the lack of specific symptoms^[2]. In many cases, individuals experience no symptoms at all^[2]. When symptoms do appear, they may point to the viral infection itself or suggest other cardiac problems such as a heart attack, making accurate diagnosis difficult^[2].

When symptoms are present, they commonly include chest pain, which can feel like pressure or discomfort in the chest area^[1]. Fatigue is another frequent complaint, where people feel unusually tired and lacking in energy^[1][4]. Shortness of breath may occur either at rest or during physical activity, making everyday tasks feel more difficult^[1][2].

Heart palpitations, which feel like the heart is racing, fluttering, or beating irregularly, are common symptoms^[1][4]. Some people experience lightheadedness or feel like they might faint^[1][4]. Swelling in the legs, ankles, and feet can develop, which happens when the weakened heart cannot pump blood efficiently^[1][4].

Flu-like symptoms may appear, including fever, headache, body aches, joint pain, and sore throat^[1]. Some individuals lose their appetite or feel weak^[4]. In more advanced stages, people may show symptoms of heart failure or experience fainting^[4]. The inability to exercise at normal levels can be a telling sign^[4].

In children, myocarditis symptoms can include difficulty breathing, rapid breathing, chest pain, rapid or irregular heartbeats, fainting, and fever^[1][6]. These symptoms develop as the inflamed heart muscle struggles to pump blood effectively throughout the body.

Prevention Strategies

Currently, there are no known lifestyle choices or medical treatments that can prevent myocarditis^[2][12]. While your lifestyle does not impact your chances of getting myocarditis, it will significantly inform your experience with the disease after diagnosis^[12]. However, since myocarditis often results from infections, reducing exposure to infectious agents represents the most practical approach to lowering risk.

Limiting contact with germs is an important step. Washing your hands regularly with soap for at least 20 seconds is a simple yet effective way to prevent infections^[12]. Using hand sanitizer when soap and water aren’t available, and staying home when sick, can help minimize your contact with disease-causing agents^[12].

Getting vaccinated against common infections can provide protection. Medical professionals recommend getting the flu shot every year and the pneumonia vaccine every five years^[12]. If you’re unsure which vaccines you need, consult your doctor for personalized recommendations^[12].

Reducing sodium intake in your diet can benefit heart health generally. Eating high amounts of salt can increase blood pressure, placing additional strain on the heart^[16]. Many doctors recommend limiting sodium consumption as part of overall cardiovascular health maintenance, which may help reduce complications if myocarditis does develop.

How Myocarditis Affects the Body

The heart is a four-chambered muscular pump about the size of an adult fist^[2]. Normally, it beats 60 to 100 times per minute, pumping blood throughout the body with each beat^[2]. The heart has two upper chambers called the right and left atria (each individual chamber is called an atrium) that receive blood returning from the body through veins^[2]. Two larger lower chambers called the right and left ventricles receive blood from the atria and pump it through arteries to the entire body^[2]. The pumping of the ventricles creates the pulse you can feel in your wrist or neck^[2].

Myocarditis disrupts this finely tuned system by causing inflammation of the myocardium, which is the heart muscle^[1][5]. Inflammation is the body’s natural way of fighting things that can harm it, such as infections or injuries^[5][14]. While inflammation normally helps protect the body, when it affects the heart muscle, it can reduce the heart’s ability to pump blood effectively^[1].

This weakening of the heart muscle makes it more difficult for the heart to pump blood normally^[4]. When the damaged heart cannot efficiently circulate blood, the rest of the body doesn’t receive adequate blood supply carrying oxygen and nutrients^[1]. In severe cases, blood clots can form in the heart, potentially leading to stroke or heart attack^[1].

Myocarditis can develop suddenly, appearing acutely, or it can be recurring or long-lasting (chronic)^[5][14]. In rare cases where the inflammation is severe, myocarditis can scar the heart muscle^[5][14]. This damage means the heart has to work harder to pump blood and oxygen around the body^[5][14]. Over time, this can result in the heart muscle becoming bigger and progressively weaker^[5][14].

Sometimes myocarditis affects the heart’s electrical system, leading to irregular heartbeats known as arrhythmias^[1][5][14]. These abnormally fast, slow, or irregular heartbeats can cause symptoms like palpitations, dizziness, or fainting^[1][4].

Myocarditis can sometimes occur together with pericarditis, which is inflammation of the lining around the heart^[5][14]. When both conditions are present simultaneously, it is sometimes called myopericarditis^[5][14]. It’s important to distinguish myocarditis from other types of heart inflammation: pericarditis affects the sac around the heart, while endocarditis is an infection or inflammation of the heart valves^[4].