Hypoplastic left heart syndrome (HLHS) is a variant of congenital heart disease which is characterized by an underdevelopment of the left sided cardiac structures (mitral valve, left ventricle, aortic valve and aorta). In HLHS, the left side of the heart is unable so support the systemic circulation so blood returning from the lungs must flow through an opening in the wall between the atria (atrial septal defect). The right ventricle pumps the blood into the pulmonary artery and blood reaches the aorta through a patent ductus arteriosus.