What is Hypoplastic Left Heart Syndrome

Hypoplastic Left Heart Syndrome (HLHS) is a rare, life-threatening congenital heart defect where the left side of the heart—including the aorta, mitral valve, and left ventricle—is severely underdeveloped and unable to pump oxygen-rich blood to the rest of the body. Because the heart cannot function normally at birth, HLHS requires immediate medical intervention, typically involving a series of staged reconstructive surgeries starting in the first days of life.

What causes Hypoplastic Left Heart Syndrome?

The exact cause of Hypoplastic Left Heart Syndrome remains largely unknown, though it is likely a combination of genetic and environmental factors. In the womb, the left side of the heart fails to grow properly, leading to a tiny, non-functional left ventricle. This structural abnormality forces the right side of the heart to do the work of both sides, pumping blood to both the lungs and the entire body. Without surgical intervention, this configuration is fatal shortly after birth.

How common is Hypoplastic Left Heart Syndrome?

Hypoplastic Left Heart Syndrome is considered a rare condition, accounting for approximately 2% to 3% of all congenital heart defects. It occurs in roughly 1 in every 4,000 to 5,000 live births. Research suggests that it affects males slightly more often than females, though it occurs in all ethnic and geographic populations worldwide.

What are the anatomical features of Hypoplastic Left Heart Syndrome?

While HLHS is a single diagnosis, it is characterized by specific structural issues that distinguish it from other heart defects:

• Mitral valve atresia or stenosis: The valve between the left atrium and left ventricle is either missing or too small.


• Left ventricle hypoplasia: The primary pumping chamber on the left side is extremely small and underdeveloped.


• Aortic valve atresia or stenosis: The valve leading from the heart to the body is restricted, impeding blood flow.


• Hypoplastic Aorta: The main artery carrying blood to the body is significantly narrower than normal.

Next steps

• Consult a pediatric cardiologist or a specialized congenital heart surgeon immediately upon diagnosis.


• Connect with the 28 members of the DiseaseMaps community living with or caring for someone with Hypoplastic Left Heart Syndrome to share experiences.


• Reach out to organizations like the Sisters by Heart or the Adult Congenital Heart Association for specialized support resources.

Medical disclaimer: This information is for educational purposes only and does not replace professional medical advice, diagnosis, or treatment from a qualified healthcare provider.

References

• NIH Genetic and Rare Diseases Information Center (GARD): Hypoplastic Left Heart Syndrome.


• Orphanet: Hypoplastic Left Heart Syndrome (ORPHA:2057).


• American Heart Association: Congenital Heart Defects - Hypoplastic Left Heart Syndrome.


• Centers for Disease Control and Prevention (CDC): Data on Hypoplastic Left Heart Syndrome.