Hypoplastic Left Heart syndrome


Hypoplastic left heart syndrome (HLH) is a severe form of congenital heart disease in which the left-sided structures of the heart (mitral valve, left ventricle aortic valve, and aorta) do not develop normally, so that blood cannot flow normally through the left side of the heart. Before babies are born, there is a communication, called the arterial duct, between the pulmonary artery and the aorta (the two main arteries of the heart). The duct closes within the first few weeks after birth. In babies with HLH, the only way blood can flow to the aorta and the body is through the duct.

HLH occurs in approximately 1 in 5,000 children. Approximately 200 diagnoses are made annually in the UK and Ireland.


Last updated April 2014 by Dr Gurleen Sharland, Consultant Fetal Cardiologist, Evelina Children’s Hospital, Guy’s and St Thomas’ NHS Foundation Trust, London, UK.

What are the symptoms?

Babies that have HLH often look normal immediately after birth, but within a few days they become breathless, appear ashen, have difficulty feeding and become very ill. Unless it is treated, this type of heart problem is usually fatal within the first days or month of life.

What are the causes?

In most cases, the cause isn’t known, but sometimes the heart abnormality can be part of a genetic syndrome.

How is it diagnosed?

In the UK, the majority of cases are now detected before birth, though in some cases the diagnosis is not made until after birth. The diagnosis is made by performing an echocardiogram (an ultrasound examination of the heart), either before or after birth.

How is it treated?

There are a series of operations available that can allow children to have a reasonable quality of life. This surgical treatment, which is performed in specialist paediatric cardiac centres, is carried out as a staged procedure in three steps.

Until the first operation is performed, the arterial duct is kept open by injection of a drug called prostin. The initial surgery is usually carried out within a few days of birth, and is called the Norwood procedure (though babies who are very small or very ill may not be suitable for the Norwood procedure initially and may be offered a different treatment to start with, called the hybrid procedure). The aim of the Norwood procedure is to use the one good pumping chamber (right ventricle) to pump blood into the main artery to the body (the aorta). The blood supply to the lung artery (pulmonary artery) is then provided by a ‘shunt’ – a tube, made of synthetic material, which is placed between the aorta and the pulmonary artery.

The second stage of surgery (bidirectional Glenn or hemi-Fontan) is usually performed between four and 12 months of age, and the third stage (Fontan or extracardiac Fontan) is usually performed between 18 months and three years.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
At present, there is no genetic test available to detect HLH. If a family has previously had a child with HLH, their risk of having another child with a heart condition is between two to five per cent.

Prenatal diagnosis
Pregnant women that have already had an affected child can be referred directly to specialist fetal cardiology centres for assessment of their baby’s heart during pregnancy. It is also possible to detect HLH at the time of the routine mid-trimester anomaly scan (usually performed between 18 to 22 weeks’ gestation). Referral is then made to a specialist centre for confirmation of diagnosis and an explanation of the problem, its implications and the management options.

Early diagnosis allows parents time to explore all options, including palliative surgery at birth, comfort care (where the decision is made to not proceed with surgical treatment) or termination of pregnancy.

Is there support?

Little Hearts Matter

Tel: 0121 455 8982
Email: info@lhm.org.uk
Website: lhm.org.uk

The Organisation is a Registered Charity in England and Wales No. 1123290. It provides information and support for families affected by any single ventricle heart condition such as hypoplastic left heart syndrome, tricuspid atresia, complex pulmonary atresia and double inlet single ventricle conditions. The Organisation has parent-to-parent support contacts, an antenatal team and a youth service team. 

Group details last reviewed December 2020.

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