Babies born with hypoplastic left heart syndrome usually are seriously ill soon after birth. Hypoplastic left heart syndrome symptoms include:

• Grayish-blue skin color (cyanosis)
• Rapid, difficult breathing
• Poor feeding
• Cold hands and feet
• Weak pulse
• Being unusually drowsy or inactive

If the natural connections between the heart's left and right sides (foramen ovale and ductus arteriosus) are allowed to close in the first few days of life in a baby with hypoplastic left heart syndrome, he or she can go into shock and may die. Signs of shock include:

• Cool, clammy skin that may be pale or gray
• A weak and rapid pulse
• Abnormal breathing that may be either slow and shallow or very rapid
• Lackluster eyes that seem to stare

A baby who is in shock may be conscious or unconscious. If you suspect your baby is in shock, immediately call 911 or your local emergency number.

Hypoplastic left heart syndrome occurs during fetal growth when the baby's heart is developing. The cause is unknown. However, if your family has one child with hypoplastic left heart syndrome, the risk of having another with a similar condition is increased.

A normal heart has four chambers, two on the right and two on the left. In performing its basic job — pumping blood throughout the body — the heart uses its left and right sides for different tasks.

The right side moves blood to the lungs. In the lungs, oxygen enriches the blood, which then circulates to the heart's left side. The left side of the heart pumps blood into a large vessel called the aorta, which circulates the oxygen-rich blood to the rest of the body.

What happens in hypoplastic left heart syndrome

In hypoplastic left heart syndrome, the left side of the heart can't properly supply blood to the body because the lower left chamber (left ventricle) is too small or in some cases may not even exist. In addition, the valves on the left side of the heart (aortic valve and mitral valve) don't work properly, and the main artery leaving the heart (aorta) is smaller than normal.

For the first several days of life, the right side of the heart can pump blood both to the lungs and to the rest of the body through a blood vessel that connects the pulmonary artery directly to the aorta (ductus arteriosus). The oxygen-rich blood returns to the right side of the heart through a natural opening (foramen ovale) between the right chambers of the heart (atria). When the foramen ovale and the ductus arteriosus are open, they are referred to as being "patent."

If the ductus arteriosus and the foramen ovale close — which they normally do after the first day or two of life — the right side of the heart has no way to pump blood out to the body. Keeping these connections open with medication is necessary for survival in the first few days of life in babies with hypoplastic left heart syndrome. This will keep blood flowing to the body until heart surgery is performed.

If you already have a child with hypoplastic left heart syndrome, you have a higher risk of having another baby with this condition or a similar condition.

Beyond family history, there are no clear risk factors for hypoplastic left heart syndrome.

Without surgery, hypoplastic left heart syndrome is fatal, usually within the first few weeks of life.

With treatment, many babies survive, although most will have complications later in life. Some of the complications may include:

• Tiring easily when participating in sports or other exercise
• Heart rhythm abnormalities (arrhythmias)
• Fluid buildup in the lungs, abdomen, legs and feet (edema)
• Growth restriction
• Formation of blood clots that may lead to a pulmonary embolism or stroke
• Developmental problems related to the brain and nervous system
• Need for additional heart surgery or transplantation