Hypoplastic Left Heart Syndrome, or HLHS, is a rare congenital heart defect where the left side of the heart is significantly under-developed. The word "congenital" simply means "present at birth". The cause of HLHS is unknown. It is primarily thought to be the result of something going wrong during the very intricate development of the heart. It is also believed that there could be a genetic component, and the risk of having another child with a similar condition is increased if one child already has HLHS.
Despite the fact that Noah has been diagnosed with this rare condition, we are hopeful because it is the most common type of single ventricle heart defect, and as a result, it is possible to detect it before the baby is born, and much is known about how to treat it. That said, single ventricle congenital heart defects affect only five out of every 100,000 live births.*
Characteristics of HLHS
The following is taken from the Mayo Clinic as it is a very good description of what happens with HLHS:
In hypoplastic left heart syndrome, the left side of the heart can't properly supply blood to the body because the lower left chamber (left ventricle) is too small or in some cases it may not even exist. In addition, the valves on the left side of the heart (aortic valve and mitral valve) don't work properly, and the main artery leaving the heart (aorta) is smaller than normal.
For the first several days of life, the right side of the heart can pump blood both to the lungs and to the rest of the body through a blood vessel that connects the pulmonary artery directly to the aorta (ductus arteriosus). The oxygen-rich blood returns to the right side of the heart through a natural opening (foramen ovale) between the right chambers of the heart (atria). When the foramen ovale and the ductus arteriosus are open, they are referred to as being "patent."
If the ductus arteriosus and the foramen ovale close — which they normally do after the first day or two of life — the right side of the heart has no way to pump blood out to the body. Keeping these connections open is necessary for survival in the first few days of life in babies with hypoplastic left heart syndrome. This will keep blood flowing to the body until the first surgical procedure is performed.
Source: Mayo Clinic
Treatment for HLHS
HLHS is dealt with today primarily by a series of three heart surgeries: the Norwood, Glenn, and Fontan. Again, the Mayo Clinic site gives a good description of what these three surgeries accomplish.