Most of what you know about myocarditis is wrong

Separating fact from fiction about heart inflammation.

by Aisha Abdullah December 25, 2023Updated January 30, 2024

An image of a red, anatomically correct heart is against a pale blue background covered in darker blue polka dots, signifying myocarditis.

Illustration: PGN

In June 2021, the CDC announced that the agency was investigating a potential link between mRNA COVID-19 vaccines and a rare heart inflammation called myocarditis. The announcement was an example of the robust vaccine safety monitoring system working exactly as it should as federal health authorities flagged, investigated, and quickly notified the public about a rare potential safety concern.

At the time, we didn’t fully understand how rare vaccine-induced myocarditis was, who was at risk, and how COVID-19 vaccines might trigger the condition. Vaccine opponents took advantage of the gap in information to spread false and misleading claims about myocarditis that persist even today.

But the reality of myocarditis post-vaccination is very different from what anti-vaccine figures claim. Here are the facts about myocarditis and COVID-19 vaccines.

What is myocarditis?

Myocarditis is inflammation of the heart muscles—it may be acute (lasting no more than two weeks) or chronic (lasting longer than two weeks). Inflammation is the body’s natural response to infection, injury, or other triggers, like toxins and certain medications.

Although myocarditis patients may experience shortness of breath, chest pain, and heart palpitations, many have no symptoms. Myocarditis can range from a mild condition that resolves with rest and over-the-counter treatments to a severe, potentially life-threatening illness that causes lasting complications, including irregular heartbeat and heart failure.

Why didn’t we hear much about myocarditis before the pandemic?

Most people first learned about myocarditis after the CDC’s announcement, but the condition existed long before the COVID-19 pandemic.

First identified in the 1740s, myocarditis was only found to be distinct from other heart muscle diseases in the 1980s. Since then, research has determined that the condition is quite rare, occurring at a global rate of around 23 per 100,000 people, although the rate varies by nation.

Myocarditis is a serious health condition that, in severe cases, requires medical attention. However, the condition is not the same as heart attacks, heart failure, or permanent heart damage, as some vaccine opponents have falsely claimed.

What causes myocarditis?

Myocarditis from any cause is rare, and the precise cause can’t always be determined. In cases with a known or suspected cause, viral infections are by far the most common trigger, accounting for up to 69 percent of cases of heart inflammation.

Enteroviruses are the most common viral cause of myocarditis, particularly Coxsackie B virus. Myocarditis can result from infections caused by herpesvirus, influenza, HIV, and adenovirus (one of the several virus families that cause colds).

Bacterial, parasitic, and fungal infections, exposure to toxins, excessive drug use, and autoimmune conditions can also trigger myocarditis.

Early in the pandemic, doctors began reporting cases of COVID-19-related myocarditis. Data soon revealed that patients with COVID-19 had nearly 16 times higher myocarditis risk than those without COVID-19. As with other kinds of myocarditis, the increased myocarditis risk associated with COVID-19 infection is even higher in adolescent and young adult males.

How are COVID-19 vaccines related to myocarditis?

mRNA COVID-19 vaccines have been linked to very rare instances of myocarditis. Experts believe that a higher-than-expected immune response to vaccination in some populations causes this vaccine-induced myocarditis.

The risk of myocarditis after COVID-19 vaccination is extremely low for all populations, around 2 per 100,000 people. As with infection-induced myocarditis, adolescent and young adult men are at higher risk, although the exact reason is unknown. Fortunately, myocarditis post-vaccination is typically mild and resolves quickly.

Overall, myocarditis risk after COVID-19 vaccination is far lower than after COVID-19 infection. Even for young males, who have the highest myocarditis risk, the protection against serious complications and hospitalization provided by COVID-19 vaccines outweighs the risk of the rare side effect.

For more information, talk to your health care provider.

This article is supported by the Centers for Disease Control and Prevention of the U.S. Department of Health and Human Services (HHS) as part of a financial assistance award to the CDC Foundation totaling $69,392,486 with 100 percent funded by CDC/HHS. The contents are those of the author(s) and do not necessarily represent the official views of, nor an endorsement, by CDC/HHS, or the U.S. Government. In addition, the CDC Foundation does not guarantee and is not responsible for the accuracy or reliability of information or content contained in this article. Moreover, the CDC Foundation expressly disclaims all liability for damages of any kind arising out of use, reference to, or reliance on any information contained within this article. This article are not intended as, and should not be interpreted by you as, constituting or implying the CDC Foundation’s endorsement, sponsorship, or recommendation of the information, products, or services found therein.