OpenMFM Patient Education

Hypoplastic Left

Heart Syndrome

A patient-friendly guide for pregnancy and newborn planning

HLHS is a serious heart condition that starts before birth. Knowing about it early helps your team plan a safer delivery, immediate newborn care, and the next steps after birth.

Also called HLHS This handout supports, not replaces, your care team's advice

What is HLHS? Big Picture

A left-sided heart condition
In **hypoplastic left heart syndrome**, the **left side of the baby's heart is too small or not fully formed**.
  • The left side of the heart normally pumps blood out to the body.
  • In HLHS, it cannot do that job well.
  • The right side of the heart has to do extra work to send blood to both the lungs and the body.
  • HLHS is a critical congenital heart defect, which means it is present at birth and needs special care soon after delivery.

What parts of the heart are affected?

Left-sided structures
  • Left ventricle: the main pumping chamber on the left side
  • Mitral valve: the valve that lets blood enter the left ventricle
  • Aortic valve: the valve that lets blood leave the left ventricle
  • Aorta: the large blood vessel that carries blood to the body
These structures may be **very small, very tight, or fully closed**. The exact pattern can be a little different from one baby to another.

How was this found?

Prenatal diagnosis
  • HLHS is often first suspected on a prenatal ultrasound.
  • It is usually confirmed with a fetal echocardiogram, which is a detailed ultrasound of the baby's heart.
  • Doctors look for:
    • a very small left ventricle
    • a larger right ventricle
    • a small aorta
    • little or no blood flow leaving the left side of the heart
Your team also looks closely at the **opening between the upper heart chambers**. If that opening is very small, a baby may become sicker more quickly after birth.

Did I cause this? Reassurance

Most parents did nothing wrong
Most of the time, parents did **nothing** to cause HLHS.
  • The exact cause is often unknown.
  • Sometimes HLHS is linked with gene or chromosome changes.
  • Your team may discuss genetic counseling or genetic testing.
This is an important question, and the answer is usually reassuring: **this is not your fault**.

What happens during pregnancy?

Team-based care
  • Your care team may include:
    • Maternal-fetal medicine
    • Pediatric cardiology
    • Pediatric heart surgery
    • Neonatology
    • Genetic counseling
  • You may need repeat fetal heart ultrasounds during pregnancy.
  • These follow:
    • heart growth
    • blood flow
    • whether the opening between the upper chambers stays wide enough
Serial fetal echocardiograms help the team watch for **changing or borderline findings** and plan ahead.

Where should my baby be delivered?

Delivery planning matters
  • A baby with HLHS should usually be delivered at or very near a hospital with pediatric heart surgery and a newborn intensive care unit.
  • In many stable pregnancies, delivery is planned near the due date, often around 39 to 40 weeks.
  • A cesarean delivery is not usually needed just because of HLHS.
  • The delivery method is usually based on regular obstetric reasons.
The goal is simple: have the **right people, medicines, and newborn support** ready at birth.

What happens after birth?

First steps in the newborn period
  • Many babies with HLHS need prostaglandin soon after birth.
  • This medicine keeps an important blood vessel open so blood can still reach the body.
  • The baby will have an echocardiogram after birth to confirm the heart anatomy.
  • Some babies may need an urgent heart catheter procedure if the opening between the upper chambers is too small.
This early period is one reason prenatal diagnosis helps. It gives the team time to prepare for the first minutes and hours after delivery.

Will my baby need surgery?

Staged reconstruction
Yes. HLHS usually requires a **series of heart surgeries**. These surgeries do not make the heart normal, but they help the **right side of the heart pump blood to the body**.
Norwood procedure Usually in the first week of life

The first major surgery after birth.

Glenn procedure Often around 4 to 6 months

Reduces some of the workload on the heart.

Fontan procedure Often around 2 to 4 years

Completes the usual staged pathway.

What is the long-term outlook?

Lifelong follow-up
  • HLHS is a serious, lifelong heart condition.
  • Children who have surgery need regular follow-up with a heart doctor.
  • Some children may have challenges with:
    • growth
    • feeding
    • learning
    • exercise tolerance
    • heart rhythm or heart function
Every baby is different. Your pediatric cardiology and heart surgery team can give the most accurate guidance for your baby's specific heart findings.

Questions to ask your care team

Bring these to your next visit
  • What type of HLHS does my baby have?
  • Is the opening between the upper heart chambers wide enough?
  • Are there any other heart or body findings?
  • Should we consider genetic testing?
  • Where should I deliver?
  • What will happen in the first hour after birth?
  • When would the first surgery be expected?
  • What support is available for our family?

Key message

Why prenatal diagnosis helps
HLHS is a serious heart condition, but **finding it before birth gives your team time to plan** the safest delivery and newborn care.
  • The goal is to have the right doctors ready.
  • The goal is to have the right medicine ready.
  • The goal is to have the right testing and heart surgery team ready.
  • Early planning helps families move from shock to preparation.
Sources: [CDC](https://www.cdc.gov/heart-defects/about/hypoplastic-left-heart-syndrome.html), [OpenMFM fetal echo teaching deck](https://openmfm.org/decks/hlhs-sonography/hlhs_sonography.html), and [Children's Hospital of Philadelphia](https://www.chop.edu/conditions-diseases/hypoplastic-left-heart-syndrome-hlhs).

Source summary provided by user on 2026-04-27. Primary cited sources: - https://www.cdc.gov/heart-defects/about/hypoplastic-left-heart-syndrome.html - https://openmfm.org/decks/hlhs-sonography/hlhs_sonography.html - https://www.chop.edu/conditions-diseases/hypoplastic-left-heart-syndrome-hlhs Render with: marp --html --theme-set ".\output\marp\OpenMFM\openmfm-patient.css" ".\output\marp\OpenMFM\Hypoplastic Left Heart Syndrome - Patient Handout.md" -o ".\output\marp\OpenMFM\Hypoplastic Left Heart Syndrome - Patient Handout.html"

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