Medical Conditions

Long QT Syndrome in Babies

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

Content reviewed against published AHA, AAP, Mayo Clinic guidelines

Editorial policy

Last reviewed:

If your baby has been diagnosed with or you suspect long qt syndrome in babies, here is what the evidence says.

The short answer

Long QT syndrome (LQTS) is an inherited heart rhythm disorder affecting the electrical system of the heart. The "QT interval" on an ECG represents the time it takes for the heart muscle to recharge between beats -- when this interval is prolonged, it can trigger dangerous rapid heart rhythms. In infants, LQTS may present as unexplained fainting, seizure-like episodes, or, in severe cases, cardiac arrest. If there is a family history of LQTS, unexplained fainting, or sudden cardiac death, your baby should be screened with an ECG.

Key takeaways

  • Long QT syndrome (LQTS) is an inherited heart rhythm disorder affecting the electrical system of the heart. The "QT interval" on an ECG represents the time it takes for the heart muscle to recharge between beats -- when this interval is prolonged, it can trigger dangerous rapid heart rhythms. In infants, LQTS may present as unexplained fainting, seizure-like episodes, or, in severe cases, cardiac arrest. If there is a family history of LQTS, unexplained fainting, or sudden cardiac death, your baby should be screened with an ECG.
  • Usually normal when: Your baby has brief breath-holding spells during crying that resolve on their own with no loss of consciousness
  • Call your doctor if: Your baby or child has fainted or lost consciousness, especially during physical activity, swimming, being startled, or emotional stress -- call 911
  • 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)

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What Parents Should Know

According to AHA, AAP, Mayo Clinic guidelines, long QT syndrome (LQTS) is an inherited heart rhythm disorder affecting the electrical system of the heart. The "QT interval" on an ECG represents the time it takes for the heart muscle to recharge between beats -- when this interval is prolonged, it can trigger dangerous rapid heart rhythms. In infants, LQTS may present as unexplained fainting, seizure-like episodes, or, in severe cases, cardiac arrest. If there is a family history of LQTS, unexplained fainting, or sudden cardiac death, your baby should be screened with an ECG. At 0-3 months, some forms of LQTS can present in the newborn period. Signs may include an unusually slow heart rate for a newborn, episodes of cyanosis (turning blue), or seizure-like activity that is actually caused by a heart rhythm problem. LQTS has been identified as a potential contributor to some cases of SIDS. Newborn ECG screening is not universally performed but may be recommended if there is a family history. If your newborn has unexplained episodes of color change, limpness, or apparent life-threatening events, an ECG should be part of the evaluation. It is generally considered normal when your baby has brief breath-holding spells during crying that resolve on their own with no loss of consciousness. However, you should contact your pediatrician promptly if your baby or child has fainted or lost consciousness, especially during physical activity, swimming, being startled, or emotional stress -- call 911.

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

Normal vs. Concerning

Usually Normal
Worth Discussing
Your baby has brief breath-holding spells during crying that resolve on their own with no loss of consciousness
Your baby or child has fainted or lost consciousness, especially during physical activity, swimming, being startled, or emotional stress -- call 911
Your child occasionally feels their heart "skip a beat" -- occasional premature beats are common and usually harmless
Your baby has had a sudden episode of going limp, unresponsive, or turning blue without explanation -- this could be a cardiac event and requires emergency evaluation
Your child has been evaluated with an ECG that shows a normal QT interval
Your child with known LQTS has a fainting episode or is not responding to you -- call 911 and begin CPR if there is no pulse
Your family has no history of unexplained fainting, drowning, seizures, or sudden cardiac death at a young age
There is a family history of Long QT syndrome, unexplained fainting, unexplained drowning, or sudden cardiac death before age 40

When to Seek Immediate Care

  • Your baby or child has fainted or lost consciousness, especially during physical activity, swimming, being startled, or emotional stress -- call 911
  • Your baby has had a sudden episode of going limp, unresponsive, or turning blue without explanation -- this could be a cardiac event and requires emergency evaluation
  • Your child with known LQTS has a fainting episode or is not responding to you -- call 911 and begin CPR if there is no pulse

By Age

What to expect by age

0-3 months

Some forms of LQTS can present in the newborn period. Signs may include an unusually slow heart rate for a newborn, episodes of cyanosis (turning blue), or seizure-like activity that is actually caused by a heart rhythm problem. LQTS has been identified as a potential contributor to some cases of SIDS. Newborn ECG screening is not universally performed but may be recommended if there is a family history. If your newborn has unexplained episodes of color change, limpness, or apparent life-threatening events, an ECG should be part of the evaluation.

3-12 months

Infants with LQTS may have episodes of pallor, sudden limpness, or loss of consciousness that can be mistaken for seizures. These episodes may occur during feeding, crying, or being startled by a loud noise. A standard 12-lead ECG is the primary screening tool. If LQTS is diagnosed, treatment with beta-blocker medications is highly effective at preventing dangerous rhythms. Genetic testing can identify the specific type of LQTS and guide treatment.

1-3 years

Toddlers with LQTS may have fainting spells, particularly triggered by excitement, exercise, being startled, or swimming. These episodes can be mistaken for breath-holding spells or seizure disorders. If your toddler has unexplained fainting, especially triggered by physical activity, emotions, or loud sounds, LQTS should be considered. Children diagnosed with LQTS are typically treated with beta-blockers and may need to avoid certain medications and intense physical activities.

3+ years

Older children with LQTS may experience fainting during exercise, swimming, or emotional stress. Some children are diagnosed only after a family member is identified with the condition. Children with LQTS should wear a medical alert bracelet, avoid certain medications (a list is maintained at crediblemeds.org), and may need to modify sports participation. With proper treatment, the risk of cardiac events is greatly reduced.

What to Tell Your Pediatrician

  • Describe when you first noticed long qt syndrome 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 there is a family history of Long QT syndrome, unexplained fainting, unexplained drowning, or sudden cardiac death before age 40.
  • Mention if your baby has had episodes of unexplained pallor, limpness, or apparent loss of consciousness.
  • 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 brief breath-holding spells during crying that resolve on their own with no loss of consciousness
  • Your child occasionally feels their heart "skip a beat" -- occasional premature beats are common and usually harmless
  • Your child has been evaluated with an ECG that shows a normal QT interval
  • Your family has no history of unexplained fainting, drowning, seizures, or sudden cardiac death at a young age
Mention at your next visit when...
  • There is a family history of Long QT syndrome, unexplained fainting, unexplained drowning, or sudden cardiac death before age 40
  • Your baby has had episodes of unexplained pallor, limpness, or apparent loss of consciousness
  • Your child has been diagnosed with a seizure disorder but seizure medications are not fully controlling the episodes
  • A family member has been newly diagnosed with LQTS and your child has not been screened
Act now when...
  • Your baby or child has fainted or lost consciousness, especially during physical activity, swimming, being startled, or emotional stress -- call 911
  • Your baby has had a sudden episode of going limp, unresponsive, or turning blue without explanation -- this could be a cardiac event and requires emergency evaluation
  • Your child with known LQTS has a fainting episode or is not responding to you -- call 911 and begin CPR if there is no pulse

What You Can Do at Home

  • Keep track of when you notice long qt syndrome in babies — noting the time of day, duration, and any triggers can help your pediatrician.
  • Remember that your baby has brief breath-holding spells during crying that resolve on their own with no loss of consciousness — 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 or child has fainted or lost consciousness, especially during physical activity, swimming, being startled, or emotional stress -- call 911.

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.

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 long qt syndrome in babies normal?
Long QT syndrome (LQTS) is an inherited heart rhythm disorder affecting the electrical system of the heart. The "QT interval" on an ECG represents the time it takes for the heart muscle to recharge between beats -- when this interval is prolonged, it can trigger dangerous rapid heart rhythms. In infants, LQTS may present as unexplained fainting, seizure-like episodes, or, in severe cases, cardiac arrest. If there is a family history of LQTS, unexplained fainting, or sudden cardiac death, your baby should be screened with an ECG.
When should I call the doctor about long qt syndrome in babies?
Your baby or child has fainted or lost consciousness, especially during physical activity, swimming, being startled, or emotional stress -- call 911 Your baby has had a sudden episode of going limp, unresponsive, or turning blue without explanation -- this could be a cardiac event and requires emergency evaluation Your child with known LQTS has a fainting episode or is not responding to you -- call 911 and begin CPR if there is no pulse
When is long qt syndrome in babies normal?
Your baby has brief breath-holding spells during crying that resolve on their own with no loss of consciousness Your child occasionally feels their heart "skip a beat" -- occasional premature beats are common and usually harmless Your child has been evaluated with an ECG that shows a normal QT interval
What causes long qt syndrome in babies?
Long QT syndrome (LQTS) is an inherited heart rhythm disorder affecting the electrical system of the heart. The "QT interval" on an ECG represents the time it takes for the heart muscle to recharge between beats -- when this interval is prolonged, it can trigger dangerous rapid heart rhythms. In infants, LQTS may present as unexplained fainting, seizure-like episodes, or, in severe cases, cardiac arrest. If there is a family history of LQTS, unexplained fainting, or sudden cardiac death, your baby should be screened with an ECG. Common explanations include: Your baby has brief breath-holding spells during crying that resolve on their own with no loss of consciousness. Your child occasionally feels their heart "skip a beat" -- occasional premature beats are common and usually harmless.
What should I mention to my pediatrician about long qt syndrome in babies?
You should mention long qt syndrome in babies at your next visit if: There is a family history of Long QT syndrome, unexplained fainting, unexplained drowning, or sudden cardiac death before age 40. Your baby has had episodes of unexplained pallor, limpness, or apparent loss of consciousness. Your child has been diagnosed with a seizure disorder but seizure medications are not fully controlling the episodes.
Is long qt syndrome in babies normal at 0-3 months?
Some forms of LQTS can present in the newborn period. Signs may include an unusually slow heart rate for a newborn, episodes of cyanosis (turning blue), or seizure-like activity that is actually caused by a heart rhythm problem. LQTS has been identified as a potential contributor to some cases of SIDS. Newborn ECG screening is not universally performed but may be recommended if there is a family history. If your newborn has unexplained episodes of color change, limpness, or apparent life-threatening events, an ECG should be part of the evaluation.
Is long qt syndrome in babies normal at 3-12 months?
Infants with LQTS may have episodes of pallor, sudden limpness, or loss of consciousness that can be mistaken for seizures. These episodes may occur during feeding, crying, or being startled by a loud noise. A standard 12-lead ECG is the primary screening tool. If LQTS is diagnosed, treatment with beta-blocker medications is highly effective at preventing dangerous rhythms. Genetic testing can identify the specific type of LQTS and guide treatment.
Should I go to the ER for long qt syndrome in babies?
Seek emergency care if your baby or child has fainted or lost consciousness, especially during physical activity, swimming, being startled, or emotional stress -- call 911, or if your baby has had a sudden episode of going limp, unresponsive, or turning blue without explanation -- this could be a cardiac event and requires emergency evaluation. When in doubt, call your pediatrician's after-hours line for guidance.
Does long qt syndrome in babies go away on its own?
In many cases, long qt syndrome in babies resolves on its own, especially when your baby has brief breath-holding spells during crying that resolve on their own with no loss of consciousness. By 3+ years, older children with LQTS may experience fainting during exercise, swimming, or emotional stress. Some children are diagnosed only after a family member is identified with the condition. Children with LQTS should wear a medical alert bracelet, avoid certain medications (a list is maintained at crediblemeds.org), and may need to modify sports participation. With proper treatment, the risk of cardiac events is greatly reduced.
AHAAAPMAYO CLINIC

References

  1. [1]American Heart Association. Long QT Syndrome. AHA, 2024. AHA
  2. [2]Schwartz PJ, et al. Guidelines for the Interpretation of the Neonatal Electrocardiogram. European Heart Journal, 2002;23:1329-1344. AAP
  3. [3]Mayo Clinic. Long QT Syndrome: Symptoms and Causes. Mayo Clinic

Doctor Visit Checklist

Bring this checklist to your next pediatrician visit to discuss Long QT Syndrome in Babies.

Things to mention

  • Describe when you first noticed long qt syndrome 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 there is a family history of Long QT syndrome, unexplained fainting, unexplained drowning, or sudden cardiac death before age 40.
  • Mention if your baby has had episodes of unexplained pallor, limpness, or apparent loss of consciousness.
  • 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

  • There is a family history of Long QT syndrome, unexplained fainting, unexplained drowning, or sudden cardiac death before age 40
  • Your baby has had episodes of unexplained pallor, limpness, or apparent loss of consciousness
  • Your child has been diagnosed with a seizure disorder but seizure medications are not fully controlling the episodes

Urgent signs to report immediately

  • Your baby or child has fainted or lost consciousness, especially during physical activity, swimming, being startled, or emotional stress -- call 911
  • Your baby has had a sudden episode of going limp, unresponsive, or turning blue without explanation -- this could be a cardiac event and requires emergency evaluation
  • Your child with known LQTS has a fainting episode or is not responding to you -- call 911 and begin CPR if there is no pulse

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

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Bottom line

Most cases of long qt syndrome in babies are normal. Talk to your pediatrician if your baby or child has fainted or lost consciousness, especially during physical activity, swimming, being startled, or emotional stress -- call 911.

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 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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