Borderline Left Heart



Borderline left heart is a congenital heart defect in which the structures that make up the left side of the heart are smaller than they should be.

Borderline left heart is variable and can range from mild to severe. It consists of at least one, but sometimes a combination of, left-sided heart defects. Coarctation of the aorta is common. Aortic stenosis, mitral stenosis, and a small left ventricle may also be present.

Borderline left heart in the fetus is also referred to as left heart hypoplasia, hypoplastic left heart complex, and Shone complex variant. The most severe cases are closely related to hypoplastic left heart syndrome (HLHS), a condition in which the left side of the heart is too small to use at birth.

Treatment will depend on the severity of the defect and is individualized to each baby. Many babies will require a surgery within the first week or two after birth, often to repair a coarctation of the aorta.

How does borderline left heart affect my baby?

In a fetus with borderline left heart, the left-sided structures of the heart are functional but smaller than normal.

Of primary concern is the degree of underdevelopment of the left-sided structures and how they grow over time. After birth, the left-side of the heart receives oxygen-rich blood from the lungs and delivers it out to the body. The mitral valve opens to allow blood to flow from the upper chamber (left atrium) to the lower left-sided chamber (left ventricle). This left ventricle relaxes to fill with blood, then squeezes to pump blood across the aortic valve, which opens to allow blood to flow into the aorta, the large artery that carries the oxygen-rich blood out to the body.

If these structures are too small after birth, blood may not be able to be delivered to the body in normal fashion.


Borderline left heart is a congenital heart defect, meaning it is present at birth. The condition likely occurs early in fetal development (during the first 8 weeks when the heart is forming). The cause is unknown.


Borderline left heart may first be diagnosed during a routine prenatal ultrasound, typically at 18 to 20 weeks. Additional testing, including fetal echocardiography, is typically needed to confirm the diagnosis and learn more about the defect.

A diagnosis during pregnancy enables your family and your healthcare team to plan ahead for the specialized treatment and cardiac expertise your baby will need at birth, optimizing outcomes.

In some cases, borderline left heart is not detected until after a baby is born. Symptoms will vary. Babies may be pale, irritable, sweaty; they can have difficulty breathing and may not feed well. A doctor may hear a heart murmur or have difficulty feeling the baby’s pulse.

When the condition is diagnosed during pregnancy, steps are taken after birth to minimize or avoid symptoms.

Specialized Evaluation and Prenatal Care

If borderline left heart is suspected or diagnosed during pregnancy, prompt referral to a fetal cardiac center is important for further evaluation and to ensure proper treatment planning.

At Texas Children’s Fetal Center, we arrange for you to visit as quickly as possible for a comprehensive assessment by a team of specialists experienced in diagnosing and treating rare congenital heart defects. Your healthcare team will include maternal-fetal medicine physicians (OB/GYNs specializing in high-risk pregnancies), fetal and pediatric cardiologists, fetal imaging experts, geneticists, congenital heart surgeons and neonatologists.

Additional testing may include:

Our specialists will then meet with you about the results, provide treatment recommendations and answer any questions your family has, to help you make the most informed decisions regarding your baby’s care and treatment.

During pregnancy, mother and baby will be closely monitored for early detection of complications, including fetal non-immune hydrops (fluid accumulation in multiple areas of the baby’s body) and fetal heart failure, requiring early delivery.

Treatment Before Birth – Chronic Maternal Hyperoxygenation

For fetuses with borderline left heart, Texas Children’s Fetal Center is the first in the country to offer a new research protocol in which mothers receive daily oxygen therapy throughout their third trimester.

By delivering extra oxygen to the mother through a face mask or nasal cannula (nose piece), we hope to increase the amount of oxygen in her blood, the amount of oxygen going to the placenta and fetus, and ultimately the amount of oxygen flowing into the fetal lungs and the left side of the fetal heart.

Improving oxygen flow to the left side of the fetal heart might improve the growth of these structures and brain development as well.  

Known as “chronic maternal hyperoxygenation,” this treatment typically involves a minimum of 8 hours of extra oxygen a day during the third trimester, starting around 26 weeks.


For the best possible outcomes, delivery should take place at a center with the highest quality congenital heart program, ensuring the expertise and resources required at birth to treat borderline left heart and, if needed, hypoplastic left heart syndrome, including an advanced neonatal intensive care unit (NICU) and cardiac intensive care unit (CICU).  

Delivery and postnatal care should be carefully planned and coordinated. Our Fetal Center team works closely with Texas Children’s Heart Center, seamlessly transitioning your baby’s care at delivery to this national leader in pediatric cardiology and heart surgery. Here, the heart specialists treating your newborn have been an integral part of their care team since before birth.

Following delivery at Texas Children’s Pavilion for Women, your baby will be transferred to Texas Children’s level IV NICU or to Texas Children’s specialized CICU to receive the highest level of care available for premature and critically ill newborns.

Treatment After Birth

Treatment after birth depends on the severity of the condition.

Newborn infants are admitted to an ICU where they are evaluated and cared for by a multidisciplinary team (cardiologists, intensivists, cardiac surgeons). Diagnostic testing, including echocardiography (cardiac ultrasound), is performed. While the workup is ongoing, the baby may be receiving a medication called prostaglandin; this is a continuous infusion delivered via an intravenous line (catheter) to help prevent a fetal vessel called the patent ductus arteriosus (PDA) from closing. This vessel helps maintain delivery of blood flow to the body when the left-sided structures are too small.

After diagnostic testing is completed, cases are presented at the Texas Children’s Heart Center conference. This is a regular meeting attended by all Heart Center members, including cardiologists, cardiac surgeons, intensivists (critical care specialists), anesthesiologists, nurse practitioners, and nurses. A treatment plan is formulated drawing from the experience and expertise of this multidisciplinary team.

Mild forms of borderline left heart may not require surgery. In more severe cases, where the aorta is too small (also called coarctation of the aorta, or aortic arch hypoplasia), a heart surgery is required, often within the first several days of life. If the mitral valve and/or aortic valve are too small, additional surgical procedures may also be necessary, either at the time of aortic arch repair, or later in infancy or childhood.

Surgical strategies include:

  • Biventricular repair – This repair, used in most cases, is a surgical strategy to improve the size and/or function of left-sided structures so that the circulation can function like normal (a two-pump system). This approach usually requires a normal or near-normal left ventricle and a reasonably developed mitral valve. It can consist of one or multiple surgeries.
  • Single-ventricle palliation – This approach is rare, used for only the most severe cases in which the left ventricle is too small or the combination of lesions is not amenable to neonatal surgery. Single-ventricle palliation involves a series of at least three heart surgeries during the first few years of life to prolong life and enable the child’s circulation to function with only one ventricle (a single-pump system).
  • Heart transplant – Very rare, only if the above strategies fail. Given the scarcity of available donors, this is not typically offered or pursued as a first-line therapy.

Postnatal Care Team

Depending on the severity of his or her condition, your baby’s postnatal care team may include:

Babies born with borderline left heart require lifelong monitoring by a cardiologist experienced in congenital heart conditions.

At Texas Children’s Heart Center, our pediatric cardiologists follow your child through adolescence, seamlessly transitioning their care at adulthood to a cardiologist who specializes in the treatment of adults with congenital heart defects

Why Texas Children’s Fetal Center?

  • A single location for expert maternal, fetal and pediatric care. Texas Children’s Hospital offers mothers and babies the specialized care required for the diagnosis and treatment of congenital heart conditions all in one location, for highly coordinated care and treatment planning.
  • A skilled, experienced team with proven outcomes. We have a dedicated team of maternal-fetal medicine specialists, fetal imaging experts, fetal and pediatric cardiologists, congenital heart surgeons, neonatologists and others who work in concert to care for you and your baby every step of the way, using proven protocols we’ve developed over the years. With their combined expertise and unified approach, this team offers the best possible care for pregnancies involving borderline left heart.
  • We care for your child’s cardiac needs at every stage of life, from fetus to adulthood. Our comprehensive approach starts with your first prenatal visit and continues through delivery, postnatal care, childhood and adulthood, thanks to one of the nation’s leading teams of fetal, pediatric and adult congenital heart specialists.

Texas Children’s – #1 in the Nation for Pediatric Cardiology and Heart Surgery

Our Fetal Cardiology Program is a collaboration between Texas Children’s Fetal Center and Texas Children’s Heart Center, ranked #1 in the nation for pediatric cardiology and heart surgery by U.S. News & World Report for consecutive years, with outcomes among the best in the nation.

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Research and Clinical Trials

Texas Children’s, together with our partner institution Baylor College of Medicine, constantly strives to seek new and better treatments for babies with congenital heart defects.

Learn more about our fetal cardiology research.

For additional information, please contact the Cardiovascular Clinical Research Core at 832-826-2064 or email sandrea@texaschildrens.org.

For more information or to schedule an appointment,

call Texas Children’s Fetal Center at 832-822-2229 or 1-877-FetalRx (338-2579) toll-free.

Our phones are answered 24/7. Immediate appointments are often available.