Left heart hypoplasia syndrome is a critical congenital heart defect. It is characterised by underdevelopment of the left side of the heart, mainly the left ventricle. Symptoms develop dynamically after birth of the newborn. Treatment consists mainly of cardiac management with preceding pharmacological treatment. If left untreated, the defect leads to death due to circulatory failure. In Poland, several centres operate with great success on children with this defect.