Interstage period: When a baby has hypoplastic left heart syndrome (HLHS), three surgeries are needed to fix the problems. The time between the first surgery and the second surgery is called the interstage period. During this period, careful daily monitoring of the baby's health is very important. Back to Articles Related Articles Hypoplastic Left Heart Syndrome Surgery: The Fontan Procedure The Fontan procedure is open-heart surgery done as the third of three surgeries to treat hypoplastic left heart syndrome (HLHS). Read More Hypoplastic Left Heart Syndrome Surgery: The Glenn Procedure The Glenn procedure is open-heart surgery done as the second of three surgeries to treat hypoplastic left heart syndrome (HLHS). Read More Hypoplastic Left Heart Syndrome Surgery: The Norwood Procedure The Norwood procedure is open-heart surgery done as the first of three surgeries to treat hypoplastic left heart syndrome (HLHS). Read More Hypoplastic Left Heart Syndrome (HLHS) Hypoplastic left heart syndrome (HLHS) is a birth defect of a baby’s heart. The left side of the heart doesn’t grow as it should, making it smaller and weaker than normal. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.