Conditions & Care
Understanding Hypoplastic Left Heart Syndrome: A Guide For Families
By Dr. Diana Rangaves, PharmD • Aug 28, 2026
Medically Reviewed by Dr. Justus Rabach, MD
(Anna Shvets/Pexels)
Receiving a complex prenatal diagnosis can quickly turn an exciting pregnancy into a whirlwind of medical choices, emotional stress and legal questions. A prominent dispute reported by ABC7 Los Angeles brought these challenges into the national spotlight, featuring a high-profile legal battle between an Alaska gestational surrogate, McKenna West, and an expecting couple from Los Angeles. After the fetus was diagnosed in utero with a rare heart condition known as hypoplastic left heart syndrome, or HLHS, the baby was born at a Dallas hospital. The case sparked widespread public conversation about how legal surrogacy agreements function alongside critical neonatal interventions.
Hypoplastic left heart syndrome is an extremely rare, critical congenital heart defect that is present at birth, in which the whole left side of an infant’s heart is severely underdeveloped and incapable of structurally pumping oxygen-rich blood to the rest of the body. If not promptly treated and a series of open-heart reconstructive surgeries are not performed during the first days of life, HLHS is invariably fatal. Families facing this diagnosis need to understand the biological mechanics of this single ventricle disorder, the prognosis for life and the current surgical pathways.
What is hypoplastic left heart syndrome?
Hypoplastic left heart syndrome is a complex congenital heart defect that is classified as a “single-ventricle” defect because the structural components of the fetus’s heart don’t form properly during the first eight weeks of fetal development, according to the Mayo Clinic
Based on data compiled by the Centers for Disease Control and Prevention (CDC), about 2% to 3% of all congenital heart defects are HLHS, and an estimated 1 in every 3,841 live births in the United States is affected. In normal cardiovascular development, the heart would act as a two-sided pump: the right side would pump deoxygenated blood to the lungs. In contrast, the muscular left side would pump oxygenated blood away from the heart to the brain and body
The left-sided heart structures, such as the left ventricle (the main pumping chamber), the ascending aorta, the aortic valve and the mitral valve, are severely underdeveloped, very small, or even closed (atretic) in babies with HLHS
What is the life expectancy of a child with hypoplastic left heart syndrome?
Traditionally, HLHS was thought to be a universally fatal defect, and was virtually always fatal at an early age in infants. The prognosis, however, has changed dramatically over the past several decades with dramatic advances in pediatric cardiothoracic surgery and neonatal intensive care
The National Institutes of Health (NIH) reported long-term registry studies indicating that the overall 5-year survival rate for infants who undergo modern 3-stage reconstructive heart surgery ranges from 70% to 75%. Thanks to the improved survival rate, many people with HLHS are now living into adolescence and adulthood; about 50% to 60% of those who have had surgery palliated survive after 20 years
Although life expectancy remains curtailed compared to the general population due to progressive single-ventricle strain, ongoing improvements in pediatric cardiology and adult congenital heart disease (ACHD) programs are continually pushing the limits of long-term survival into the third and fourth decades of life
What’s happening in your body
During fetal life, oxygenation is provided by the mother’s placenta, and blood does not flow through the underdeveloped left heart; instead, it flows around it through two natural fetal vascular connections, the foramen ovale, a hole between the upper chambers of the heart, and the ductus arteriosus, a blood vessel connecting the pulmonary artery directly to the aorta
The problem starts in the first hours or days after birth when these fetal shunts start to close on their own, according to research at the Mayo Clinic
When the ductus constricts, blood from the baby’s single working right ventricle, which pumps at low pressure to the lungs, must now be pumped to the lungs and the whole body
Blood circulation slows to the rest of the body, depriving vital organs of oxygen and nutrients to a great extent. This overload results in a very quick cardiovascular collapse, in severe metabolic acidosis, in cyanosis (blue/greyish coloring of skin and lips), and in acute cardiogenic shock
Causes of hypoplastic left heart syndrome
The precise single cause of hypoplastic left heart syndrome is unknown, but it occurs early in pregnancy as a combination of genetic and environmental factors
Dr. Justus Rabach, MD, tells Blavity Health, “Poor blood supply in the womb can also prevent proper development of the heart. If the baby’s heart valves are too small at a very early stage of pregnancy, there is not enough blood to flow through, so the left side of the heart does not stretch out and remains small and underdeveloped.”
Genetics is considered a major factor in the development of this condition. It occurs more frequently in infants with certain chromosomal abnormalities, such as Turner syndrome, Trisomy 13, Trisomy 18 or 22q11.2 deletion syndrome, according to the Cleveland Clinic
The problem can also result from changes in certain genes. The genes that normally guide the growth of the heart’s walls and valves, such as NOTCH1, NKX2-5 and GATA4, are often inherited in families with a history of small left heart chambers
Health risks and complications
If the surgeries are successful, life with a single functioning pumping chamber is a continual health risk and presents health issues
The single heart chamber can wear out and weaken over time. It was only designed to circulate blood a short distance to the lungs, and if it is made to circulate blood throughout the body for many years, it becomes a burden and can cause heart failure
The scar tissue that forms as a result of the multiple surgeries may also interfere with the heart’s normal rhythm. This causes risky abnormal heart rhythms that may require special heart medications or the implantation of a pacemaker
When blood pressure in the veins is high, it can cause fluid to leak where it is not supposed to be. Leakage into the gut leads to severe diarrhea and malnutrition; leakage into the airways can result in rubbery fluid plugs that block the lungs
Over time, this sustained high pressure in the veins also works its way back into the liver. The congestion slowly damages the liver tissue and may cause severe damage
Children who spend long periods on life support, with low oxygen levels as infants, and who have undergone many major operations are at increased risk for learning challenges, movement difficulties and daily problem-solving
Can a woman with HLHS have a baby?
Pregnancy in a woman with hypoplastic left heart syndrome who has had three-stage Fontan surgical palliation is an extremely high-risk medical situation requiring specialized and multidisciplinary cardio-obstetric care
Clinical guidelines from the American Heart Association (AHA) state that pregnancy increases maternal blood volume by up to 50% and that cardiac output increases significantly. This enormous amount of blood leaves a single-ventricle heart at serious risk for acute maternal heart failure, serious arrhythmias and maternal thromboembolism and miscarriage
Successful pregnancies have been achieved in stable adult Fontan survivors with good ventricular function through close monitoring. However, many cardiology teams do not support pregnancy and recommend other alternatives, such as surrogacy or adoption, to protect the life of the mother
What to do about an HLHS diagnosis
Treating hypoplastic left heart syndrome starts right after birth in an intensive care unit for children’s hearts. The baby is immediately administered medicines through an IV. This medicine helps keep a particular blood vessel open, allowing the rest of the body to receive oxygen-carrying blood
Once the baby gets stable, heart surgeons will do three operations over the next several years. The surgeries restore the heart to the point where it can have only one functional side to pump blood to the rest of the body
The first occurs within two weeks of life. Doctors reconstruct the primary blood vessel and temporarily attach a small tube, which provides blood flow to the lungs
The second operation is performed at four to six months of age. The large vein from the upper part of the body is directly connected to the lung pipes, and the used blood flows into the lungs of its own accord
The last one is performed when the child is between two and four years old. The large vein from the bottom half of the body is also joined to the lungs by the surgeon. This separates used blood from fresh blood, so that only oxygen-rich blood is sent to the body by the heart
When to see a doctor
HLHS is commonly diagnosed by a routine 18- to 20-week pregnancy ultrasound. If it is not detected before delivery, the newborn requires immediate medical attention in the newborn’s first hours or days of life
If a fetus is diagnosed with hypoplastic left heart syndrome (HLHS) on a mid-pregnancy anatomy ultrasound or fetal echocardiogram, arrange for delivery at a tertiary pediatric hospital with a Level IV Neonatal and Pediatric Cardiac Intensive Care Unit (PCICU). Direct transport to a specialized congenital heart surgical center improves early survival outcomes and avoids transport delay
If the baby’s lips, tongue, or nails are blue, gray, or pale; if the baby’s nostrils are flaring and their chest is sucking in; if the baby is very sleepy, having trouble waking up to feed or eating poorly; or if the hands and feet are cold and sweaty with very weak pulses in the legs, get emergency help immediately
“The heart is a very complex organ and sometimes in utero it just doesn’t form right—the valve may not form, a ventricle may not form, an artery or vein may be abnormal,” says Mark Sklansky, MD, medical director of Pediatric and Fetal Cardiology Outreach in the Smidt Heart Institute and Cedars-Sinai Guerin Children’s
Bottom line
Hypoplastic left heart syndrome is an extremely rare and severe congenital heart disease in which the left side of the heart does not form properly, and normal blood flow to the body is not possible after birth. Although this was an inevitable death sentence in the past, today pediatric cardiac care uses prostaglandin infusions to keep the child alive and a three-stage series of surgical reconstruction procedures (Norwood, Glenn, and Fontan procedures) to give the child a greater than 70% chance of surviving for five years. Management of this single-ventricle condition is lifelong, with monitoring by specially trained adult congenital heart disease cardiologists to maintain a healthy ventricle and preserve organ function.
Frequently Asked Questions
How rare is a hypoplastic left heart?
Hypoplastic left heart syndrome is quite rare, occurring in approximately 1 out of every 3,841 live births and representing roughly 2% to 3% of all congenital heart anomalies
Do all HLHS patients need a heart transplant?
No, not all HLHS patients require a heart transplant; the majority are successfully managed through the standard three-stage surgical palliation process, reserving orthotopic heart transplantation for cases of severe single-ventricle heart failure
Citations
Ozebek K. Amid legal battle, LA couple’s surrogate gives birth in Texas to baby with heart defect. ABC7 Los Angeles. Published August 14, 2026. https://abc7.com/post/la-couples-surrogate-mckenna-west-gives-birth-texas-baby-heart-defect/19675521/
Mayo Clinic. Hypoplastic left heart syndrome – symptoms and causes. Mayo Clinic. Published January 21, 2025. https://www.mayoclinic.org/diseases-conditions/hypoplastic-left-heart-syndrome/symptoms-causes/syc-20350599
CDC. Data and Statistics. Congenital Heart Defects (CHDs). Published May 15, 2024. https://www.cdc.gov/heart-defects/data/index.html
Kačar P, Tamborrino PP, Iannaccone G, et al. Hypoplastic left heart syndrome (HLHS) becomes of age: Assessing the young adult with HLHS including the neoaorta/aortic arch. International Journal of Cardiology Congenital Heart Disease. 2024;19:100555. doi:10.1016/j.ijcchd.2024.100555
Mayo Clinic. About Hypoplastic Left Heart Syndrome (HLHS). Mayo Clinic. Published 2018. https://www.mayo.edu/research/centers-programs/todd-karen-wanek-family-program-hypoplastic-left-heart-syndrome/about/about-hlhs
Cleveland Clinic. Genetic Disorders: What Are They, Types, Symptoms & Causes. Cleveland Clinic. Published 2021. https://my.clevelandclinic.org/health/diseases/21751-genetic-disorders
Sanghavi M, Rutherford JD. Cardiovascular Physiology of Pregnancy. Circulation. 2014;130(12):1003-1008. doi:10.1161/circulationaha.114.009029
