HLHS main

Several abnormalities of development occur on the left side of the heart in hypoplastic left heart syndrome:

The valve from the left top heart chamber to the left bottom heart chamber is poorly developed (mitral stenosis) to not formed (mitral atresia).
The bottom left heart chamber is poorly developed (left ventricular hypoplasia), the valve from the bottom left heart chamber to the main artery is poorly developed (aortic stenosis) to not formed (aortic atresia).
The main artery leaving the left side of the heart, the aorta, is underdeveloped.
The aorta is narrowed as well (coarctation of the aorta).

Leroy, Callow, and George (1996) conclude the heart defect "is called a syndrome because several areas of the heart's left side are affected. HLHS is a very serious problem. Not all children are affected in the same way or to the same degree. Few children survive more than 1 or 2 weeks without surgery. While HLHS affects about two children in 10,000, the cause of HLHS is not known."

LeRoy et al. (1996) explain: "survival for a baby with HLHS depends on a connection between the pulmonary artery and the aorta. This connection is called a patent ductus arteriosus (PDA). This is a normal connection in all babies that usually closes when the baby is 24-48 hours old. For babies with HLHS, the PDA allows some blood to flow from the pulmonary artery into the aorta. If the PDA closes, the baby will not have enough blood going out to the body and will become very sick. Usually a drug called prostaglandin will be started to help keep the PDA open."

The surgical options for HLHS include cardiac transplantation and the Norwood Procedure. The Norwood Procedure is a series of operations designed to have the blue (unoxygenated) blood flow directly to the lungs and then use the existing right heart to pump the red (oxygenated) blood to the body.