Myocarditis: What You Should Know

Medically Reviewed by Poonam Sachdev on January 10, 2024
7 min read

Myocarditis is inflammation of the heart muscle (also called myocardium). Researchers think that it affects 1.5 million people around the world each year. This means that 1 or 2 out of every 10,000 people have it. It can be acute (symptoms last less than 1 month) or chronic (symptoms last more than 1 month) and range from mild to severe.

Many people who get myocarditis are otherwise healthy. Several things can lead to it, with infection being the most common cause. The best way to prevent myocarditis is to treat infections quickly and take action to prevent them.

Infections, especially viral infections, are the biggest cause of myocarditis.

When you have an infection, your body makes cells to fight the virus. These cells release chemicals. If the disease-fighting cells enter your heart, some chemicals they release can aggravate your heart muscle. This causes inflammation.

Some infections that can cause myocarditis include:

  • Viruses
    • Adenovirus (the common cold)
    • SARS-CoV-2, the virus that causes COVID-19
    • Coxsackie B viruses (diarrhea)
    • Cytomegalovirus (CMV)
    • Echovirus (diarrhea)
    • Epstein-Barr virus (EBV), known as mononucleosis or “mono”
    • Hepatitis B
    • Hepatitis C
    • Herpes
    • HIV
    • Influenza (flu)
    • Parvovirus B-19, which causes Fifth disease
    • Rubella
    • Varicella (chicken pox)
  • Bacteria
  • Parasites
    • Toxoplasma gondii (toxoplasmosis)
    • Trypanosoma cruzi (Chagas disease)
  • Fungi
    • Candida (oral thrush)
    • Aspergillus
    • Histoplasma

Myocarditis can also be caused by an autoimmune disease that causes inflammation  throughout your body, such as lupus or rheumatoid arthritis.

Other causes include certain chemicals or allergic reactions to toxins such as:

  • Alcohol
  • Drugs such as cocaine
  • Lead and other heavy metals
  • Spider bites
  • Wasp stings
  • Snakebites
  • Carbon monoxide
  • Radiation

Some medications can cause myocarditis, including:

  • Chemotherapy and radiation therapy
  • Medications for your heart
  • Antidepressants and other psychiatric drugs
  • Medications for seizures, such as benzodiazepines
  • Antibiotics
  • Medications for weight loss
  • Diuretics
  • Vaccines, including the COVID-19 vaccine

It is very rare for the COVID-19 vaccine to cause myocarditis. Only 2 out of every 100,000 people who get the vaccine get myocarditis. In comparison, if you’re hospitalized for COVID-19, it’s more common to get myocarditis -- about 226 out of every 100,000 people.

Young men and people assigned male at birth (aged 16-29) are more likely to get myocarditis as a side effect of the COVID-19 vaccine. For 95% of people who get this side effect, myocarditis is mild and symptoms go away in a few days. Still, a COVID-19 illness is much more likely to cause severe and life-threatening myocarditis.

You are more likely to get myocarditis if you:

  • Are male or were assigned male at birth
  • Are a young adult
  • Drink a lot of alcohol
  • Tend to get inflammation
  • Get certain medical treatments (such as dialysis, radiation, implanted heart devices, and central venous lines)
  • Have certain medical conditions (such as HIV/AIDS, chronic kidney disease, diabetes, skin or chest injuries, and eating disorders)

Myocarditis often has no symptoms. In fact, most people recover and never even know they had it.

If you do have symptoms, they may include:

  • Shortness of breath
  • Abnormal heartbeat, which causes fainting in rare cases
  • Lightheadedness
  • A sharp or stabbing chest pain or pressure, which may spread to your neck and shoulders
  • Fatigue
  • Signs of infection, such as
  • Painful joints
  • Swollen joints, legs, feet, or neck veins
  • Small amounts of urine
  • Loss of appetite
  • Weakness

Infants are at high risk for myocarditis because they are exposed to viruses during childbirth but don’t have a fully developed immune system yet. They tend to have more severe symptoms, including:

  • Pale skin
  • Difficulty eating
  • Weakness
  • Irritability
  • Breathing problems

Older children also get myocarditis. Sometimes, symptoms appear after an illness, but this isn’t always the case. Older children might have:

  • Pale skin
  • Rapid or difficult breathing
  • Fever
  • Cough
  • Cold hands or feet
  • Tiredness
  • Chest pain
  • Fainting

If you or your child have these symptoms, your doctor will check for an abnormal or rapid heartbeat, fluid in your lungs, or leg swelling.

Call your doctor right away if you have symptoms of myocarditis. If you have or had an infection, it’s more likely that you have the condition. Seek immediate medical care if your symptoms are severe. If your symptoms such as chest pain, trouble breathing, or swelling have gotten worse since you were told you have myocarditis, call 911 or go to the hospital.

Your doctor may order tests such as:

  • Blood tests to check for infection, antibodies, or blood cell counts
  • A chest X-ray so they can see your heart, lungs, and other chest structures
  • An electrocardiogram (EKG) to record your heart's electrical activity
  • A heart ultrasound (echocardiogram) to make an image of your heart and its structures
  • A PET scan to view your organs and tissues
  • Cardiac catheterization to see how well your heart is working
  • A CT or CAT scan of the heart

Sometimes, doctors order cardiac MRI scans or heart muscle biopsies to help confirm myocarditis. These tests also can help diagnose myocarditis in children.

Sometimes, mild myocarditis gets better on its own. But other times, you might need medical treatment.

If possible, your doctor will treat the cause of the myocarditis (for example, by prescribing medications for lupus).

Usually, you’ll be given medicines to help your heart work better. Examples include:

  • ACE inhibitors .These lower your blood pressure so your heart doesn’t have to work as hard.
  • Beta-blockers. These slow down your heart rate and lower blood pressure.
  • Corticosteroids. These calm down inflammation in the heart.
  • Diuretics . These can help decrease fluid build-up caused by a weakened heart.
  • Intravenous immunoglobulin. These are antibodies, or infection-fighting proteins, delivered through an IV.

Your doctor will probably suggest rest or reduced activity. They might put you on a low-salt diet to keep fluid from building up. If you have mild myocarditis, it will often get better with just medication and rest.

Your doctor also might take steps to prevent or control complications (such as blood clots). If you have complications, you might be hospitalized. Serious cases of myocarditis may require other treatments, such as:

  • Extracorporeal membrane oxygenation (ECMO). For this treatment, a machine removes carbon dioxide from and adds oxygen to your blood.
  • Implantable cardioverter-defibrillator (ICD). A surgeon implants this device near your heart. When your heart beats irregularly, the device restores its normal rhythm by delivering a small shock.
  • Intra-aortic balloon pump. This device uses a tiny balloon to help the heart pump more blood.
  • Pacemaker. This device, similar to an ICD, helps regulate your heartbeat.
  • Ventricular assist device (VAD). This machine helps a weakened heart to pump blood.

In very rare cases, severe heart damage might require a heart transplant.

Your outlook depends on:

  • The cause of your myocarditis
  • Your overall health
  • Complications you have, if any

Many people recover completely, with no complications or long-term damage. Others have chronic myocarditis. Either way, follow-up care can help keep track of any ongoing problems. It's also important to know that myocarditis can come back, although it’s not common.

There are many ways to take care of your heart. Here are some tips:

  • Limit the amount of salt you eat.
  • Avoid drinking.
  • Don’t smoke.
  • Don’t exercise until your doctor says it’s okay.
  • Ask your doctor if you need to limit the amount of liquid you drink.
  • Keep in touch with your doctor. Take your medicines as prescribed, schedule regular follow-up appointments, and get suggested follow-up tests.

It’s important to continue these healthy habits even after myocarditis has gone away.

If left untreated, myocarditis may lead to heart failure. This is when your heart has trouble pumping blood. Myocarditis also can cause cardiomyopathy (when the heart muscle weakens or the structure of the heart muscle changes) and pericarditis (inflammation of the pericardium, the sac covering the heart). In rare cases, it can lead to other problems, such as:

  • Heart attack or stroke
  • Lung problems
  • Arrhythmia
  • Cardiogenic shock

Myocarditis and cardiomyopathy are the leading causes of heart transplants in the U.S. In very rare cases, myocarditis can lead to sudden death.

Myocarditis is often a treatable condition. With medical care, many people have a full recovery. Severe myocarditis requires immediate medical treatment. Call 911 if you have chest pain, difficulty breathing, or rapid heartbeat.

What are COVID-19 myocarditis symptoms?

Symptoms of myocarditis include heart palpitations, weakness, chest pain, fever, and shortness of breath. These symptoms can range in severity. Some people don’t have any symptoms.

What does the beginning of myocarditis feel like?

Early or mild myocarditis might not cause any symptoms. When it does, it could feel like chest pain, tiredness, irregular heartbeat, or shortness of breath.

Does myocarditis go away?

Mild cases of myocarditis sometimes get better on their own. Other cases need medical treatment and follow-up care.

What percentage of COVID-19 patients get myocarditis?

For every 1,000,000 people that get COVID-19, about 40 get myocarditis, so just 0.004%. But for people who are hospitalized for COVID-19, the prevalence is higher: 226 out of 100,000. In comparison, myocarditis affects only 2 people out of every 100,000 who get the COVID-19 vaccine.