In hypoplastic left heart syndrome, the entire left side of the heart - including the aorta, aortic valve, left ventricle and mitral valve - is underdeveloped. Blood returning from the lungs must flow through an opening in the wall between the atria, called an atrial septal defect. The right ventricle pumps the blood into the pulmonary artery and blood reaches the aorta through a patent ductus arteriosus (see above).

The baby often seems normal at birth, but will come to medical attention within a few days of birth as the ductus closes. Babies with this syndrome become ashen, have rapid and difficult breathing and have difficulty feeding. This heart defect is usually fatal within the first days or months of life without treatment.

Although this defect is not correctable, some babies can be treated with a series of operations, often leading to a heart transplant later in childhood. Until an operation is performed, the ductus is kept open by intravenous (IV) medication. Because these operations are complex and different for each patient, you need to discuss all the medical and surgical options with your child's doctor. Your doctor will help you decide which is best for your baby.

If you and your child's doctor elect to undergo surgery, the surgery will be performed in several stages. The first stage, called the Norwood procedure, allows the right ventricle to pump blood to both the lungs and the body. It must be performed soon after birth. The final stage(s) has many names including bi-directional Glenn, Fontan operation and lateral tunnel. These operations create a connection between the veins returning blue blood to the heart and the pulmonary artery. The overall goal of the operation is to allow the right ventricle to pump only oxygenated blood to the body and to prevent or reduce mixing of the red and blue blood. Some infants require several intermediate operations to achieve the final goal.

At our current stage of knowledge, most doctors believe that the operations described above for hypoplastic left heart are palliative (temporary) and that a heart transplant will sooner or later be required, perhaps in later chilhood or early adulthood. Although it does provide the child with a heart that has a normal structure, the infant will require lifelong supervision and medications to prevent rejection. Many other problems related to transplants could develop, and you should discuss these with your doctor.

Children with hypoplastic left heart syndrome require lifelong follow-up by a paediatric cardiologist for repeated checks of how their heart is working. Virtually all the children will require heart medicines.

People with hypoplastic left heart syndrome, before and after treatment, are at risk for getting an infection on the heart's valves (endocarditis). To help prevent this, they'll need to take antibiotics before certain dental and surgical procedures. Good dental hygiene also lowers the risk of endocarditis. For more information about dental hygiene and preventing endocarditis, ask your paediatric cardiologist and your dentist.