DefinitionHypoplastic left heart syndrome occurs when parts of the left side of the heart (mitral valve, left ventricle, aortic valve, and aorta) do not develop completely. The condition is congenital (present at birth).Alternative NamesHLHSCauses, incidence, and risk factorsHypoplastic left heart is a rare type of congenital Heart disease. It is more common in males than in females.As with most congenital heart defects, there is no known cause. Approximately 10% of patients with hypoplastic left heart syndrome also have other birth defects.The problem develops before birth when there is not enough growth of the left ventricle and other structures, including the:Aorta -- the blood vessel that carries oxygen-rich blood from the left ventricle to the entire bodyEntrance and exit of the ventr