Your child’s diagnosis
Hypoplastic left heart syndrome (HLHS)
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How blood flows
Hypoplastic left heart syndrome (HLHS)
The same region in both views. The usual view is a comparison, not a treatment result.
HLHS · the right pump supports both routes
- Less oxygen
- Mixed blood
- More oxygen
Step 1 of 4
The left side is underdeveloped
The left ventricle is too small for the usual pumping job. Left-sided valves and the aorta may also be very small or closed.
How to read this map
Follow the arrows to see connections. This is a map, not the shape or position of a heart. Both sides work together; the story follows one part at a time. A crossing with a white gap is not a connection; a dot marks a junction. With story controls focused, use left/right arrows, Home or End.
An example before treatment, with an open atrial connection and arterial duct. No usual forward route through the left ventricle is shown. Left-sided valve arrangements vary. This is not a Norwood, Glenn or Fontan circulation. Vessel sizes and route widths are symbolic.
Colours describe this example: blue means less oxygen, red more oxygen, and purple mixing. Blood is always red in real life. Line widths and animation do not measure flow, pressure, oxygen saturation or severity.
Diagram sources and scope
An example before treatment, with an open atrial connection and arterial duct. No usual forward route through the left ventricle is shown. Left-sided valve arrangements vary. This is not a Norwood, Glenn or Fontan circulation. Vessel sizes and route widths are symbolic.
Original Heart Up Close connection map · Source check: 26 October 2026 · Independent clinical review pending.
Hypoplastic left heart syndrome (HLHS)
- The left side is underdeveloped. The left ventricle is too small for the usual pumping job. Left-sided valves and the aorta may also be very small or closed.
- Lung return crosses to the right. Oxygen-rich blood returns to LA, then crosses an atrial opening to RA. Here it joins blood returning from the body.
- The right pump supplies the lung artery. The right ventricle pumps the mixed blood into the pulmonary artery. One route continues towards the lungs.
- An open duct also supplies the body. Some blood passes from the pulmonary artery through the open duct to the aorta and body. These temporary connections are essential before treatment.
An example before treatment, with an open atrial connection and arterial duct. No usual forward route through the left ventricle is shown. Left-sided valve arrangements vary. This is not a Norwood, Glenn or Fontan circulation. Vessel sizes and route widths are symbolic.
02
Diagnosis and care
Diagnosis and tests
A pregnancy heart scan may find HLHS. Sometimes it is found after birth when a baby becomes unwell, breathless, unusually tired or struggles to feed. Finding it during pregnancy gives the maternity and heart teams time to discuss where and how the baby will be born and what care is needed straight away. Families need time and support to understand the results.
An echocardiogram, or echo, is an ultrasound scan of the heart. Scans during pregnancy and after birth show the chambers, valves and blood flow. After birth, the team checks oxygen levels and other signs of blood reaching the body. Later scans or catheter tests, using thin tubes in blood vessels, may help plan treatment.
Ask what is known now and what can only be clearer after birth.
Care and follow-up
Medicine can keep the arterial duct open while care is planned. Operations in stages can change blood flow so the right ventricle supplies the body. Later stages send blood returning from the body directly towards the lungs. These operations do not create the usual two-pump heart.
The first operation may be a Norwood, which creates a new route to supply the body, or another procedure suited to the baby.
The team needs to discuss your baby’s options, risks and the likely demands of treatment. Surgery may not be suitable for every baby. Comfort care, which focuses on keeping the baby comfortable with support for the family, is also an option to discuss. An individual child’s long-term needs are uncertain. Families should have clear explanations, emotional support and chances to ask again without pressure.
Daily life
Ask for a named contact and a written plan for birth or discharge. If you need to check your child’s health at home, ask the team to explain the equipment. They should tell you which results mean you need help and how to get it. Little Hearts Matter supports families affected by single ventricle conditions, where one chamber does the work of the main pump.
03
Questions to ask
Save the questions you want to take to your next appointment. You can edit them in your Journal.
- Which parts of our baby’s heart are small or not fully formed, and could you show us what that means for blood flow?
- What care will our baby need immediately after birth, and where should the birth and early care take place?
- Which care options are appropriate for our baby, and can you explain the benefits, uncertainties and demands of each?
- What would each stage of treatment change, and what heart differences or care needs would remain afterwards?
- What practical and emotional support can we access while we consider the options and make decisions for our baby?
Sources and review
Sources checked 9 October 2026. Independent clinical review pending.
- British Heart Foundation: Hypoplastic left heart syndrome
Accessed 9 October 2026
- Children’s Heart Federation: Hypoplastic Left Heart Syndrome (HLHS) Information Sheet
Accessed 9 October 2026
- Little Hearts Matter: Hypoplastic Left Heart Syndrome
Accessed 9 October 2026