Medical Conditions

Myocarditis (Heart Muscle Inflammation) in Babies

Medically reviewed by Dr. Michael Okonkwo, MD, FAAP · Board-Certified Neonatologist

Content reviewed against published AAP, AHA, Mayo Clinic guidelines

Editorial policy

Last reviewed:

If your baby has been diagnosed with or you suspect myocarditis (heart muscle inflammation) in babies, here is what the evidence says.

The short answer

Myocarditis is inflammation of the heart muscle, most often caused by a viral infection. In babies and young children, it can develop during or after a common viral illness (such as a cold or stomach bug) and may cause the heart to weaken and pump less effectively. Symptoms include rapid breathing, poor feeding, excessive sleepiness, pallor, and sometimes a rapid or irregular heartbeat. Myocarditis can range from mild to life-threatening. If your baby seems unusually ill after a viral infection with signs of breathing difficulty or poor feeding, seek immediate medical attention.

Key takeaways

  • Myocarditis is inflammation of the heart muscle, most often caused by a viral infection. In babies and young children, it can develop during or after a common viral illness (such as a cold or stomach bug) and may cause the heart to weaken and pump less effectively. Symptoms include rapid breathing, poor feeding, excessive sleepiness, pallor, and sometimes a rapid or irregular heartbeat. Myocarditis can range from mild to life-threatening. If your baby seems unusually ill after a viral infection with signs of breathing difficulty or poor feeding, seek immediate medical attention.
  • Usually normal when: Your baby has a common cold or viral illness with mild symptoms that are improving day by day
  • Call your doctor if: Your baby has rapid or labored breathing, grayish or pale skin, poor feeding, and seems very lethargic -- these are signs of possible heart failure and require emergency evaluation
  • Varies by age — see the age-by-age breakdown below
“Fever itself is not an illness — rather, it is a sign or symptom that the body is fighting an infection. Fever stimulates certain defenses, such as the white blood cells, which attack and destroy invading bacteria.”
— Fever and Your Child, American Academy of Pediatrics (AAP)

This is one of the most common questions parents ask. Searching for answers means you care.

What Parents Should Know

According to AAP, AHA, Mayo Clinic guidelines, myocarditis is inflammation of the heart muscle, most often caused by a viral infection. In babies and young children, it can develop during or after a common viral illness (such as a cold or stomach bug) and may cause the heart to weaken and pump less effectively. Symptoms include rapid breathing, poor feeding, excessive sleepiness, pallor, and sometimes a rapid or irregular heartbeat. Myocarditis can range from mild to life-threatening. If your baby seems unusually ill after a viral infection with signs of breathing difficulty or poor feeding, seek immediate medical attention. At 0-3 months, neonatal myocarditis is rare but can be severe. It is most often caused by enteroviruses (such as coxsackievirus) acquired during or shortly after birth. Symptoms may include poor feeding, lethargy, rapid breathing, grunting, grayish skin color, and a rapid heartbeat. Newborn myocarditis can progress rapidly to heart failure and cardiogenic shock. Any newborn who appears significantly unwell, especially with breathing difficulty and poor perfusion, needs emergency evaluation. It is generally considered normal when your baby has a common cold or viral illness with mild symptoms that are improving day by day. However, you should contact your pediatrician promptly if your baby has rapid or labored breathing, grayish or pale skin, poor feeding, and seems very lethargic -- these are signs of possible heart failure and require emergency evaluation.

Sources: [1], [2], [3]

Normal vs. Concerning

Usually Normal
Worth Discussing
Your baby has a common cold or viral illness with mild symptoms that are improving day by day
Your baby has rapid or labored breathing, grayish or pale skin, poor feeding, and seems very lethargic -- these are signs of possible heart failure and require emergency evaluation
Your baby has a slightly faster heart rate during fever, which returns to normal when the fever resolves
Your child complains of severe chest pain, has an irregular heartbeat, or becomes faint or unresponsive -- call 911
Your child is eating, drinking, and playing normally despite having a mild respiratory illness
Your baby or child suddenly worsens after seeming to recover from a viral illness, with new signs of breathing difficulty or inability to feed
Your baby is recovering from a virus and energy levels are gradually returning to normal
Your baby seems to be taking longer than expected to recover from a viral illness and remains unusually tired

When to Seek Immediate Care

  • Your baby has rapid or labored breathing, grayish or pale skin, poor feeding, and seems very lethargic -- these are signs of possible heart failure and require emergency evaluation
  • Your child complains of severe chest pain, has an irregular heartbeat, or becomes faint or unresponsive -- call 911
  • Your baby or child suddenly worsens after seeming to recover from a viral illness, with new signs of breathing difficulty or inability to feed

By Age

What to expect by age

0-3 months

Neonatal myocarditis is rare but can be severe. It is most often caused by enteroviruses (such as coxsackievirus) acquired during or shortly after birth. Symptoms may include poor feeding, lethargy, rapid breathing, grunting, grayish skin color, and a rapid heartbeat. Newborn myocarditis can progress rapidly to heart failure and cardiogenic shock. Any newborn who appears significantly unwell, especially with breathing difficulty and poor perfusion, needs emergency evaluation.

3-12 months

Infants may develop myocarditis after common viral infections. Signs include new-onset rapid breathing, poor feeding or refusal to eat, excessive sweating (especially during feeds), irritability, and unusual sleepiness. The baby may appear pale or grayish. Because these symptoms overlap with many common illnesses, myocarditis can be initially missed. If your baby seems to be recovering from a virus but then worsens or develops breathing difficulty, seek medical evaluation promptly.

1-3 years

Toddlers with myocarditis may present with poor appetite, vomiting, abdominal pain, fatigue, and rapid breathing. They may become less active, not want to play, or want to be held constantly. A previously active toddler who suddenly becomes very lethargic or has difficulty breathing should be evaluated. Myocarditis in toddlers is diagnosed with ECG, chest X-ray, echocardiogram, and blood tests (troponin and BNP levels).

3+ years

Older children can describe symptoms such as chest pain, difficulty breathing, and feeling their heart beating fast or irregularly. Myocarditis in older children may follow a respiratory or gastrointestinal illness. Children may report that they feel very tired and cannot keep up with activities. If your child complains of chest pain, has difficulty breathing, or becomes unusually fatigued after a viral illness, medical evaluation is important.

What to Tell Your Pediatrician

  • Describe when you first noticed myocarditis (heart muscle inflammation) in babies and how it has changed over time.
  • Note your baby's current age and which age-specific patterns you are seeing.
  • Mention if your baby seems to be taking longer than expected to recover from a viral illness and remains unusually tired.
  • Mention if your baby's breathing seems faster than normal even after a fever has resolved.
  • Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
  • Bring a list of any questions or observations you want to discuss at the appointment.

What Should You Do?

When to take action

Probably normal when...
  • Your baby has a common cold or viral illness with mild symptoms that are improving day by day
  • Your baby has a slightly faster heart rate during fever, which returns to normal when the fever resolves
  • Your child is eating, drinking, and playing normally despite having a mild respiratory illness
  • Your baby is recovering from a virus and energy levels are gradually returning to normal
Mention at your next visit when...
  • Your baby seems to be taking longer than expected to recover from a viral illness and remains unusually tired
  • Your baby's breathing seems faster than normal even after a fever has resolved
  • Your child complains of chest discomfort or seems to tire more easily than usual after a recent illness
Act now when...
  • Your baby has rapid or labored breathing, grayish or pale skin, poor feeding, and seems very lethargic -- these are signs of possible heart failure and require emergency evaluation
  • Your child complains of severe chest pain, has an irregular heartbeat, or becomes faint or unresponsive -- call 911
  • Your baby or child suddenly worsens after seeming to recover from a viral illness, with new signs of breathing difficulty or inability to feed

What You Can Do at Home

  • Keep track of when you notice myocarditis (heart muscle inflammation) in babies — noting the time of day, duration, and any triggers can help your pediatrician.
  • Remember that your baby has a common cold or viral illness with mild symptoms that are improving day by day — this is generally within the range of normal.
  • At 0-3 months, focus on observation rather than intervention unless your pediatrician advises otherwise.
  • Follow any care instructions from your pediatrician. Keep a written log of symptoms to bring to appointments.
  • While monitoring at home, seek immediate care if your baby has rapid or labored breathing, grayish or pale skin, poor feeding, and seems very lethargic -- these are signs of possible heart failure and require emergency evaluation.

Congenital Heart Defect Signs in Babies

Congenital heart defects (CHDs) are the most common type of birth defect, affecting about 1 in 100 babies. They range from small holes in the heart that may close on their own to complex defects requiring multiple surgeries. Early detection through pulse oximetry screening and recognizing key signs — such as blue skin, rapid breathing, poor feeding, and failure to gain weight — is critical. Advances in surgery have dramatically improved survival and quality of life.

Baby Heart Murmur - Innocent vs Concerning

Heart murmurs are very common in children - up to 75% of children will have an audible murmur at some point. The vast majority are "innocent" or "functional" murmurs, meaning there is no structural heart problem. These murmurs are simply the sound of blood flowing normally through the heart and are more audible during fever, illness, or excitement. A smaller number of murmurs indicate a structural heart difference that may need monitoring or treatment. Your pediatrician can usually distinguish between the two and will refer for an echocardiogram if there is any concern.

My Baby Turns Blue (Cyanosis)

Blue or purple discoloration limited to a baby's hands and feet (acrocyanosis) is very common in newborns and usually harmless, caused by immature circulation. However, blue coloring of the lips, tongue, face, or trunk (central cyanosis) is always a medical emergency that requires immediate evaluation, as it may indicate a heart or lung problem.

Triage

Breathing Difficulty Triage

Assess breathing concerns and know when to seek emergency care.

Milestone

Month-by-Month Development

Detailed monthly development guides from birth through 24 months.

Guide

When to Call the Doctor

General guide on when to call the pediatrician, visit urgent care, or go to the ER.

Frequently asked questions

Is myocarditis (heart muscle inflammation) in babies normal?
Myocarditis is inflammation of the heart muscle, most often caused by a viral infection. In babies and young children, it can develop during or after a common viral illness (such as a cold or stomach bug) and may cause the heart to weaken and pump less effectively. Symptoms include rapid breathing, poor feeding, excessive sleepiness, pallor, and sometimes a rapid or irregular heartbeat. Myocarditis can range from mild to life-threatening. If your baby seems unusually ill after a viral infection with signs of breathing difficulty or poor feeding, seek immediate medical attention.
When should I call the doctor about myocarditis (heart muscle inflammation) in babies?
Your baby has rapid or labored breathing, grayish or pale skin, poor feeding, and seems very lethargic -- these are signs of possible heart failure and require emergency evaluation Your child complains of severe chest pain, has an irregular heartbeat, or becomes faint or unresponsive -- call 911 Your baby or child suddenly worsens after seeming to recover from a viral illness, with new signs of breathing difficulty or inability to feed
When is myocarditis (heart muscle inflammation) in babies normal?
Your baby has a common cold or viral illness with mild symptoms that are improving day by day Your baby has a slightly faster heart rate during fever, which returns to normal when the fever resolves Your child is eating, drinking, and playing normally despite having a mild respiratory illness
What causes myocarditis (heart muscle inflammation) in babies?
Myocarditis is inflammation of the heart muscle, most often caused by a viral infection. In babies and young children, it can develop during or after a common viral illness (such as a cold or stomach bug) and may cause the heart to weaken and pump less effectively. Symptoms include rapid breathing, poor feeding, excessive sleepiness, pallor, and sometimes a rapid or irregular heartbeat. Myocarditis can range from mild to life-threatening. If your baby seems unusually ill after a viral infection with signs of breathing difficulty or poor feeding, seek immediate medical attention. Common explanations include: Your baby has a common cold or viral illness with mild symptoms that are improving day by day. Your baby has a slightly faster heart rate during fever, which returns to normal when the fever resolves.
What should I mention to my pediatrician about myocarditis (heart muscle inflammation) in babies?
You should mention myocarditis (heart muscle inflammation) in babies at your next visit if: Your baby seems to be taking longer than expected to recover from a viral illness and remains unusually tired. Your baby's breathing seems faster than normal even after a fever has resolved. Your child complains of chest discomfort or seems to tire more easily than usual after a recent illness.
Is myocarditis (heart muscle inflammation) in babies normal at 0-3 months?
Neonatal myocarditis is rare but can be severe. It is most often caused by enteroviruses (such as coxsackievirus) acquired during or shortly after birth. Symptoms may include poor feeding, lethargy, rapid breathing, grunting, grayish skin color, and a rapid heartbeat. Newborn myocarditis can progress rapidly to heart failure and cardiogenic shock. Any newborn who appears significantly unwell, especially with breathing difficulty and poor perfusion, needs emergency evaluation.
Is myocarditis (heart muscle inflammation) in babies normal at 3-12 months?
Infants may develop myocarditis after common viral infections. Signs include new-onset rapid breathing, poor feeding or refusal to eat, excessive sweating (especially during feeds), irritability, and unusual sleepiness. The baby may appear pale or grayish. Because these symptoms overlap with many common illnesses, myocarditis can be initially missed. If your baby seems to be recovering from a virus but then worsens or develops breathing difficulty, seek medical evaluation promptly.
Should I go to the ER for myocarditis (heart muscle inflammation) in babies?
Seek emergency care if your baby has rapid or labored breathing, grayish or pale skin, poor feeding, and seems very lethargic -- these are signs of possible heart failure and require emergency evaluation, or if your child complains of severe chest pain, has an irregular heartbeat, or becomes faint or unresponsive -- call 911. When in doubt, call your pediatrician's after-hours line for guidance.
Does myocarditis (heart muscle inflammation) in babies go away on its own?
In many cases, myocarditis (heart muscle inflammation) in babies resolves on its own, especially when your baby has a common cold or viral illness with mild symptoms that are improving day by day. By 3+ years, older children can describe symptoms such as chest pain, difficulty breathing, and feeling their heart beating fast or irregularly. Myocarditis in older children may follow a respiratory or gastrointestinal illness. Children may report that they feel very tired and cannot keep up with activities. If your child complains of chest pain, has difficulty breathing, or becomes unusually fatigued after a viral illness, medical evaluation is important.
AAPAHAMAYO CLINIC

References

  1. [1]American Academy of Pediatrics. Myocarditis. HealthyChildren.org. AAP
  2. [2]American Heart Association. Myocarditis in Children. Circulation, 2014;129(1):115-128. AHA
  3. [3]Mayo Clinic. Myocarditis: Symptoms and Causes. Mayo Clinic

Doctor Visit Checklist

Bring this checklist to your next pediatrician visit to discuss Myocarditis (Heart Muscle Inflammation) in Babies.

Things to mention

  • Describe when you first noticed myocarditis (heart muscle inflammation) in babies and how it has changed over time.
  • Note your baby's current age and which age-specific patterns you are seeing.
  • Mention if your baby seems to be taking longer than expected to recover from a viral illness and remains unusually tired.
  • Mention if your baby's breathing seems faster than normal even after a fever has resolved.
  • Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
  • Bring a list of any questions or observations you want to discuss at the appointment.

Observations to share

  • Your baby seems to be taking longer than expected to recover from a viral illness and remains unusually tired
  • Your baby's breathing seems faster than normal even after a fever has resolved
  • Your child complains of chest discomfort or seems to tire more easily than usual after a recent illness

Urgent signs to report immediately

  • Your baby has rapid or labored breathing, grayish or pale skin, poor feeding, and seems very lethargic -- these are signs of possible heart failure and require emergency evaluation
  • Your child complains of severe chest pain, has an irregular heartbeat, or becomes faint or unresponsive -- call 911
  • Your baby or child suddenly worsens after seeming to recover from a viral illness, with new signs of breathing difficulty or inability to feed

My notes

From ismybabyalright.com — free, evidence-based baby health guides

All content follows our editorial policy and is reviewed against published clinical guidelines.

2,705 evidence-based guides6 authoritative medical sources5 medical advisory board members

Related Resources

Breathing TriageEar Infection TriageWell-Baby Visit PrepEmergency ContactsBaby Tracker

Bottom line

Most cases of myocarditis (heart muscle inflammation) in babies are normal. Talk to your pediatrician if your baby has rapid or labored breathing, grayish or pale skin, poor feeding, and seems very lethargic -- these are signs of possible heart failure and require emergency evaluation.

Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.

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Congenital Heart Defect Signs in Babies

Congenital heart defects (CHDs) are the most common type of birth defect, affecting about 1 in 100 babies. They range from small holes in the heart that may close on their own to complex defects requiring multiple surgeries. Early detection through pulse oximetry screening and recognizing key signs — such as blue skin, rapid breathing, poor feeding, and failure to gain weight — is critical. Advances in surgery have dramatically improved survival and quality of life.

Baby Heart Murmur - Innocent vs Concerning

Heart murmurs are very common in children - up to 75% of children will have an audible murmur at some point. The vast majority are "innocent" or "functional" murmurs, meaning there is no structural heart problem. These murmurs are simply the sound of blood flowing normally through the heart and are more audible during fever, illness, or excitement. A smaller number of murmurs indicate a structural heart difference that may need monitoring or treatment. Your pediatrician can usually distinguish between the two and will refer for an echocardiogram if there is any concern.

My Baby Turns Blue (Cyanosis)

Blue or purple discoloration limited to a baby's hands and feet (acrocyanosis) is very common in newborns and usually harmless, caused by immature circulation. However, blue coloring of the lips, tongue, face, or trunk (central cyanosis) is always a medical emergency that requires immediate evaluation, as it may indicate a heart or lung problem.

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