The term hypoplastic left heart syndrome was introduced by Noonan and Nadas in 1958 inorder to describe the features of combined aortic atresia and mitral atresia. This syndrome is found in children very early in their development; it can be noticed when the baby is still inside of the mother. In babies with hypoplastic left heart syndrome, the left side of the heart basically cannot pump oxygen-rich blood to the body properly. The oxygen poor blood and the oxygen rich blood are mixed together, which causes the blue skin tone. As the baby grows, the defects in the heart make it very difficult for the body to get the oxygen it needs to survive.The basic problems of a heart that is affected by this syndrome include:

• Underdeveloped left ventricle

• Mitral atresia (the absence of the valve that connects the left atrium to the left ventricle) or a small mitral valve

• Aortic atresia (the absence of the valve that connects the  left ventricle to the aorta) or a small aortic valve

• Ascending part of the aorta is underdeveloped

Although these factors are common there is a spectrum of congenital heart defects associated with this syndrome. A common physiology of HLHS is that the systemic circulation is driven by the right ventricle via a patent ductus arteriosus. To fix this problem there are certain treatments. Surgeries are common treatments. There are three main surgeries: Norwood Procedure, Glenn Procedure, and Fontan Procedure

       This entire problem has led to many medical developments and continued research. There have been advances in utero diagnosis and fetal catheter-based interventation. It has been found that this syndrome is in fact not rare. The incidence among patients with congenital heart disease had been reported to be between 4 and 9% and the treatment for this syndrome has grown to the point where many can be saved.