May also be called: HLHS Hypoplastic (HI-puh-plas-tik) left heart syndrome (HLHS) is a rare and serious defect in which the structures of the left side of the heart (the left ventricle, the mitral valve, and the aortic valve) are underdeveloped. As a result, blood cannot be adequately pumped throughout the body. More to Know Hypoplastic left heart syndrome is present at birth (congenital) and has no known cause. It is usually diagnosed within the first few days of life. Without surgery to repair the heart, HLHS is fatal. Symptoms of HLHS include blue or gray skin color (cyanosis), rapid breathing, pounding heart, shortness of breath, cold hands and feet, weak pulse, unusual drowsiness and poor feeding. Once diagnosed with HLHS, most babies will undergo a series of three operations beginning shortly after birth and ending at 3 years of age. For some babies, heart transplant is the best option if a donated organ is available. Keep in Mind While many babies now survive HLHS, they need to be monitored closely by a cardiologist for the rest of their lives. Many complications can occur with HLHS and sometimes additional heart surgery or even heart transplant may be necessary as children born with HLHS get older. All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts. Back to Articles Related Articles Congenital Heart Defects Heart defects happen when there's a problem with a baby's heart development during pregnancy. Most heart defects can be treated during infancy. Read More Coarctation of the Aorta Coarctation of the aorta (COA) is a narrowing of the aorta, the major blood vessel that carries blood away from the heart to the body. Read More Patent Ductus Arteriosus (PDA) The ductus arteriosus is a blood vessel that connects two major arteries before birth and normally closes after a baby is born. If it stays open, the result is a condition called patent ductus arteriosus (PDA). Read More Atrial Septal Defect (ASD) Atrial septal defect (ASD) — also known as a "hole in the heart" — is a type of congenital heart defect. Most ASDs are diagnosed and treated successfully. Read More Ventricular Septal Defect (VSD) Ventricular septal defect (VSD) — also known as a "hole in the heart" — is a congenital heart defect. Most VSDs are diagnosed and treated successfully. Read More When Your Child Needs a Heart Transplant If your child needs a heart transplant, you're probably feeling lots of emotions. Fortunately, many kids who undergo heart transplants go on to live normal, healthy lives. Read More When Your Baby Has a Birth Defect If your child has a birth defect, you don't have to go it alone - many people and resources are available to help you. Read More Heart and Circulatory System The heart and circulatory system are our body's lifeline, delivering blood to the body's tissues. Brush up on your ticker with this body basics article. 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.