Myocarditis

Your heart muscle normally contracts rhythmically and efficiently, pumping blood throughout your body without you giving it a thought. Myocarditis is inflammation of this heart muscle, typically triggered by viral infections, though many other causes exist. The inflammation can range from mild cases causing barely noticeable symptoms to severe disease leading to heart failure or dangerous rhythm problems. Many people recover completely within weeks to months, their hearts returning to normal function. Others develop permanent heart damage requiring lifelong treatment. What makes myocarditis particularly challenging is its unpredictability—similar triggers can cause vastly different outcomes in different people.

Overview

Myocarditis is inflammation of the heart muscle tissue. When your heart muscle becomes inflamed, it can’t contract as forcefully, potentially impairing your heart’s ability to pump blood effectively. The inflammation can also disrupt electrical signals, causing rhythm problems.

The condition affects people of all ages, from infants to elderly adults, though it’s most commonly diagnosed in young to middle-aged adults. Men are affected somewhat more often than women.

Severity varies enormously. Some people have such mild myocarditis that they never seek medical attention, attributing their fatigue and mild chest discomfort to the viral illness that caused it. Others develop severe symptoms including heart failure, dangerous rhythms, or even sudden death. Between these extremes are people with moderate disease causing noticeable symptoms but recovering with supportive care.

Viral infections are the most common trigger. The same viruses causing colds, flu, and stomach bugs can occasionally affect the heart. Your immune system responds to the virus, but this inflammatory response sometimes damages heart muscle even as it fights the infection.

The heart can be the only organ affected, or myocarditis can occur as part of a wider inflammatory condition affecting multiple body systems. Sometimes inflammation involves the pericardium—the sac surrounding the heart—along with the muscle itself, a condition called myopericarditis.

Recovery patterns vary. Many people recover completely within weeks to months, their heart function returning to normal. Some develop chronic inflammation leading to dilated cardiomyopathy—a weakened, enlarged heart. A small percentage experience fulminant myocarditis—severe, rapidly progressing disease requiring intensive support but often followed by complete recovery if the patient survives the acute phase.

The unpredictability makes myocarditis challenging. Two people with the same viral infection might have completely different outcomes—one recovers quickly while the other develops serious complications. We don’t fully understand why some people develop myocarditis from infections that cause only minor illness in millions of others.

Causes

Many triggers can cause myocarditis, though viral infections are by far the most common in developed countries.

• Common viruses that can affect the heart include enteroviruses like coxsackievirus and echovirus, which also cause hand-foot-and-mouth disease and stomach bugs. Adenoviruses causing respiratory infections can trigger myocarditis. Parvovirus B19, which causes fifth disease in children, affects the heart in some people. Influenza viruses occasionally cause myocarditis. Even common cold viruses can rarely affect the heart.
• COVID-19 can cause myocarditis, though this appears less common than initially feared during the pandemic. Most COVID-related heart inflammation is mild.
• The inflammation develops through two mechanisms. First, the virus directly infects heart muscle cells, damaging them. Second, and often more important, your immune system responds vigorously to fight the infection. This immune response, while trying to eliminate the virus, can cause collateral damage to heart tissue.
• Bacterial infections less commonly cause myocarditis in developed countries but remain important causes globally. Lyme disease from tick bites can affect the heart. Strep throat, if untreated, can lead to rheumatic fever affecting the heart. Certain bacterial infections, particularly if they enter the bloodstream, can cause heart inflammation.
• Autoimmune diseases where your immune system mistakenly attacks your own tissues can cause myocarditis. Conditions including lupus, rheumatoid arthritis, and inflammatory bowel disease sometimes affect the heart.
• Medications and drugs can trigger myocarditis. Certain antibiotics, some chemotherapy drugs, antipsychotics, and anticonvulsants have been implicated. Cocaine and methamphetamine use can cause severe myocarditis. Even some medications used to treat abnormal heart rhythms can paradoxically cause heart inflammation.
• Vaccines rarely cause myocarditis. This gained attention with COVID-19 vaccines, particularly mRNA vaccines in young men. However, the risk is very low—roughly 10 to 20 cases per million vaccine doses—and vaccine-related myocarditis is typically mild, with excellent recovery rates. The risk of myocarditis from COVID-19 infection itself is several times higher than from vaccination.
• Toxins including heavy metals and certain chemicals can damage heart muscle and cause inflammation.
• Giant cell myocarditis is a rare, aggressive form with unknown cause that often requires heart transplantation.
• In many cases, despite thorough evaluation, no specific cause is identified. These cases are called idiopathic myocarditis.

Symptoms

Myocarditis symptoms vary dramatically based on severity and can mimic many other conditions.

• Many people with mild myocarditis have no specific heart symptoms, attributing fatigue and general malaise to the viral illness that triggered it. They recover without ever knowing their heart was affected.
• When symptoms occur, they often develop days to weeks after a viral illness. You might think you’re recovering from a cold or flu, then notice new symptoms suggesting your heart is affected.
• Chest pain or discomfort is common, often described as sharp or aching in the center or left side of the chest. Unlike heart attack pain from blocked arteries, myocarditis chest pain is often worsened by lying flat and improved by sitting forward. It can vary with breathing or movement.
• Shortness of breath develops as inflammation impairs your heart’s pumping ability. Initially noticeable only during activity, it can progress to occurring at rest or when lying flat in more severe cases.
• Fatigue is often profound and out of proportion to what you’d expect from a simple viral illness. You feel exhausted with minimal activity.
• Palpitations or awareness of your heartbeat occur as inflammation disrupts electrical signals. You might feel extra beats, skipped beats, or rapid heartbeat.
• Swelling in the legs, ankles, or abdomen develops if heart function becomes significantly impaired, causing fluid retention.
• Fever might persist or recur as inflammation continues, even after the initial viral illness seemed resolved.
• Rapid heartbeat even at rest suggests your heart is working harder to maintain adequate blood flow.
• In children, symptoms might be less specific—fussiness, poor feeding, rapid breathing, or seeming generally unwell without clear cause.
• Sudden onset of severe symptoms—difficulty breathing, chest pain, fainting, or collapse—indicates potentially life-threatening myocarditis requiring immediate emergency care.
• Some cases present with sudden cardiac arrest as the first manifestation, particularly in young athletes who collapse during sports. This tragic presentation emphasizes why chest pain, shortness of breath, or palpitations during or after viral illness should never be ignored, especially in young, previously healthy people.

Diagnosis

Diagnosing myocarditis is challenging because symptoms can be vague and mimic other conditions. No single test definitively diagnoses all cases.

• Your medical history provides crucial clues. Recent viral illness, new chest pain or shortness of breath, and symptoms appearing days to weeks after being sick all suggest possible myocarditis.
• Physical examination might reveal rapid heartbeat, abnormal heart sounds, signs of fluid retention, or evidence of heart failure, though examination can be completely normal in mild cases.
• Blood tests check for markers of heart muscle damage and inflammation. Troponin, a protein released when heart muscle is injured, is typically elevated in myocarditis. However, troponin also rises with heart attacks, so elevation alone doesn’t distinguish between the two. Other markers of inflammation including C-reactive protein are often elevated.
• Electrocardiogram often shows abnormalities including changes suggesting inflammation or injury, but findings are nonspecific. The test also identifies dangerous rhythm problems that can occur with myocarditis.
• Echocardiography visualizes heart structure and function. It shows whether the heart is pumping normally, identifies areas of muscle that aren’t contracting well, checks for fluid around the heart, and evaluates chamber sizes. Many people with myocarditis have reduced pumping function, though some have normal echocardiograms despite having the condition.
• Cardiac MRI is the most useful imaging test for myocarditis. This provides detailed images showing inflammation and injury patterns characteristic of myocarditis, distinguishes it from heart attacks, and identifies the extent of heart muscle involvement. However, MRI isn’t always necessary for diagnosis and isn’t available at all medical centers.
• Coronary angiography might be performed to rule out heart attack, particularly in adults where blocked arteries are possible. Finding normal coronary arteries in someone with symptoms and elevated troponin suggests myocarditis rather than heart attack.
• Heart muscle biopsy, where tiny tissue samples are removed through a catheter for microscopic examination, definitively diagnoses myocarditis by showing inflammation and damaged cells. However, biopsy is invasive with small risks and is usually reserved for severe cases, cases not improving with treatment, or when specific rare forms of myocarditis are suspected.
• Viral testing through blood tests sometimes identifies the specific virus, though by the time myocarditis develops, the virus often isn’t detectable.

Treatment

Treatment focuses on supporting your heart while inflammation resolves and managing complications.

• For mild cases, rest is crucial. Avoid strenuous activity for several months—at minimum three to six months—even if you feel better. Exercise during acute myocarditis can worsen heart damage and increase risk for dangerous rhythms. This restriction is particularly important for athletes who must abstain from competitive sports until the heart fully recovers.
• Medications support heart function and reduce workload. ACE inhibitors or ARBs help the heart pump more efficiently and reduce strain. Beta-blockers slow heart rate and reduce oxygen demands. Diuretics eliminate excess fluid if retention develops. These standard heart failure medications support your heart while it heals.
• Anti-inflammatory medications are controversial. Unlike pericarditis where anti-inflammatory drugs clearly help, their role in myocarditis is less certain. Some doctors prescribe them for certain types of myocarditis, while others avoid them fearing they might interfere with the healing process.
• Treating underlying causes is important when identified. Bacterial infections require antibiotics. Autoimmune-related myocarditis might need immunosuppressive drugs. Stopping medications causing the inflammation is essential.
• For severe cases with heart failure, more aggressive support is needed. Hospitalization in intensive care units allows close monitoring and advanced treatments. Intravenous medications support blood pressure and heart function. Mechanical support devices can temporarily take over the heart’s pumping function while it recovers. These devices range from balloon pumps to complete mechanical hearts supporting circulation for days to weeks.
• For fulminant myocarditis—the most severe, rapidly progressing form—aggressive mechanical support is often needed. Paradoxically, patients who survive this critical phase with intensive support often recover completely, their hearts returning to normal function.
• Heart transplantation becomes an option if the heart doesn’t recover despite maximum support and chronic severe heart failure develops.
• Monitoring for dangerous rhythms is crucial. Continuous heart monitoring in the hospital detects rhythm problems requiring immediate treatment. Some patients need temporary pacemakers if inflammation affects the heart’s electrical system.

What Happens If Left Untreated

Untreated myocarditis can lead to serious complications, though outcomes vary enormously.

• Many people with mild myocarditis recover spontaneously even without specific treatment, particularly if they rest and avoid strenuous activity. The inflammation resolves on its own within weeks to months.
• However, without appropriate rest and medical supervision, several problems can develop. Continuing strenuous activity during acute inflammation can worsen heart damage. Athletes who continue training or competing with undiagnosed myocarditis face increased risk for sudden death.
• Heart failure can develop if inflammation significantly impairs pumping function. Without treatment, this worsens progressively as the heart struggles to meet the body’s needs.
• Dangerous heart rhythms can occur, particularly fast rhythms from the lower chambers that can cause sudden death. Inflammation creates electrically unstable tissue prone to these life-threatening rhythms.
• Chronic heart muscle damage might develop if inflammation persists or causes extensive scarring. This leads to dilated cardiomyopathy—a chronically weakened, enlarged heart requiring lifelong treatment. Some people who recover from acute myocarditis later develop heart failure years down the line from residual damage.
• Sudden death is the most tragic outcome, occurring in a small percentage of cases, particularly in young athletes with unrecognized myocarditis who continue intense physical activity.
• Blood clots can form in poorly contracting heart chambers, potentially causing strokes.

What to Watch For

If you’ve been diagnosed with myocarditis, certain symptoms require immediate attention.

• Seek emergency care for worsening chest pain, severe shortness of breath, or difficulty breathing, particularly if these come on suddenly.
• Call emergency services if you faint or feel like you’re about to faint. This suggests dangerous rhythm problems or severely inadequate blood flow.
• Contact your doctor promptly for new or worsening swelling in legs or abdomen, which suggests developing or worsening heart failure.
• Report new palpitations or feeling that your heart is beating very rapidly or irregularly.
• Notify your doctor about persistent fever despite treatment or symptoms that worsen rather than improve after several days of treatment.
• If you have a recent viral illness and develop chest pain, shortness of breath, or palpitations—particularly if symptoms worsen with activity—seek medical evaluation promptly. Don’t assume these are just part of the viral illness.
• For athletes, any chest pain, unusual shortness of breath, or palpitations during or after exercise requires immediate evaluation before returning to sports.

Recovery and Long-Term Outlook

Recovery from myocarditis varies widely between individuals.

• Many people, particularly young, previously healthy individuals with mild myocarditis, recover completely within weeks to months. Their heart function returns to normal, and they resume all normal activities including vigorous exercise and competitive sports.
• During recovery, gradual return to activity is important. After several months of rest, progressive increase in activity under medical supervision allows safe return to normal life. For athletes, this typically involves a structured program of gradually increasing exercise intensity over several months while monitoring heart function.
• Follow-up testing including echocardiograms and sometimes cardiac MRI assesses recovery. Serial tests over months show whether heart function is improving, stable, or worsening.
• Some people develop chronic heart problems. If heart function doesn’t fully recover, you might need ongoing medications and activity restrictions. Regular cardiology follow-up becomes lifelong.
• Recurrence is uncommon but possible. Some people experience repeated episodes of myocarditis, particularly those with autoimmune triggers.
• Pregnancy considerations are important for women who’ve had myocarditis. If heart function is normal, pregnancy is usually safe. If residual heart dysfunction persists, pregnancy carries increased risks and requires careful monitoring.
• The overall outlook has improved significantly with modern supportive care. Most people with myocarditis survive and many recover completely. Even those requiring intensive support for severe disease can have excellent long-term outcomes.

Key Points

• Myocarditis is inflammation of the heart muscle, most commonly triggered by viral infections, though many other causes exist including autoimmune conditions, medications, and toxins.
• Symptoms vary from none to severe heart failure or sudden death. Common symptoms include chest pain, shortness of breath, fatigue, and palpitations developing during or after viral illness.
• Rest is crucial during acute illness. Avoiding strenuous activity for several months allows the heart to heal and reduces risk for dangerous complications. This is particularly important for athletes.
• Many people, especially young and previously healthy individuals, recover completely with their hearts returning to normal function within weeks to months.
• Some develop chronic heart problems including dilated cardiomyopathy requiring lifelong treatment. Factors predicting recovery aren’t fully understood, making the condition’s course somewhat unpredictable.
• Sudden death can occur, particularly in young athletes with unrecognized myocarditis who continue intense training. Any chest pain, unusual shortness of breath, or palpitations during or after viral illness requires evaluation before returning to sports.
• Cardiac MRI is the most useful imaging test for diagnosing myocarditis and assessing extent of heart involvement.
• Heart muscle biopsy definitively diagnoses the condition but is reserved for severe cases or when specific rare forms are suspected.
• Vaccine-related myocarditis, while receiving significant attention, is rare and typically mild with excellent recovery. The risk from the infection itself is generally higher than from vaccination.
• Work closely with a cardiologist during and after myocarditis. These specialists monitor recovery, guide return to activity, and determine whether long-term treatment is necessary. While myocarditis is a serious diagnosis, the outlook for most people, particularly with appropriate care and adequate rest during the acute phase, is good. The key is recognizing the condition early, providing appropriate supportive care, ensuring adequate rest during healing, and monitoring recovery to ensure the heart returns to normal function before resuming full activities. For those with residual heart dysfunction, modern heart failure treatments allow most people to live active, fulfilling lives despite ongoing heart problems.

Reference: Myocarditis