Hypoplastic 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).

Hypoplastic left heart is a rare type of congenital heart disease. It is more common in males than in females.

The problem develops before birth when there is not enough growth of the left ventricle and other structures (aortic and mitral valves that guard the exit and entrance of the ventricle and the aorta, the blood vessel that carries oxygenated blood from the left ventricle to the entire body).

In patients with this condition, the left side of the heart is unable to send enough blood to the body. As a result, the right side of the heart must maintain the circulation for both the lungs and the body. This extra workload eventually causes the heart to fail.

The only possibility of survival is a connection between the right and the left side of the heart its blood vessels, through which blood may pass. This is called a shunt. Babies are normally born with two of these connections (the foramen ovale and the ductus arteriosus), which normally close on their own a few days after birth.

If ductus arteriosus is allowed to close in a baby with hypoplastic left heart syndrome, however, the patient will quickly die because no blood will be pumped to the body.

As with most congenital heart defects, there is no known cause. Around 10% of patients with hypoplastic left heart syndrome will have other birth defects.

Initially, a newborn with hypoplastic left heart may appear normal. Symptoms usually occur in the first few hours of life, although it may take up to a few days to develop symptoms. These symptoms may include:

• Lethargy
• Poor suckling and feeding
• Shortness of breath
• Rapid breathing
• Cold extremities
• Enlarged liver
• Poor pulse
• Pounding heart
• Bluish (cyanosis) or poor skin color
• Sudden death

In healthy newborns, bluish color occurs in hands and feet as a response to cold (this reaction is called peripheral cyanosis).

However, a bluish color observed in the chest or abdomen, lips, and tongue is abnormal (called central cyanosis) because it reflects lack of adequate levels of oxygen in the blood. This is secondary to the heart malformation and circulatory malfunction. Central cyanosis often increases with crying.

A physical exam may show signs of heart failure, liver enlargement, rapid breathing, and lethargy. Additionally, the pulse at various locations (wrist, groin, and others) is usually very weak. There are usually abnormal heart sounds when listening to the chest.

Tests may include:

• ECG shows enlargement of the right ventricle of the heart
• X-ray of the chest may show signs of other birth defects
• Echocardiogram
• Cardiac catheterization