A normal heart is divided into four hollow 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 into vessels called pulmonary arteries, leading to the lungs. In the lungs, oxygen enriches the blood, which circulates to the heart's left side in blood vessels called pulmonary veins. The left side of the heart pumps blood into a large vessel called the aorta. Branching off from the aorta are numerous other vessels that circulate blood to the rest of the body.

SLIDE SHOW

  A peek at the secret life of your heart
 
 

A baby's heart starts beating just 22 days after conception. At that point, the heart has a simple tube shape. Between days 22 and 24, however, the heart begins to bend to the right and fold in on itself to form a loop. By 28 days after conception, looping is completed and the tube has a vaguely heart-like shape with structures corresponding to the heart's two sides and the large blood vessels that carry blood in and out of them.

Most likely, you and your partner won't even realize you're pregnant when these important changes are occurring. But if the genetic messages that direct the growth and movement of early heart cells are scrambled, part of the heart muscle may fail to develop. Or if the process of bending and looping doesn't go exactly the way it's supposed to, the heart may form abnormal connections to the large vessels leading to and from the lungs.

Many heart defects can be detected before birth by a test called fetal echocardiography. It uses sound waves to create a picture of your baby's heart. If the heart is beating too slowly or quickly, medications can usually fix the problem before the heart starts to fail. If a heart defect can't be treated before birth, doctors can use the information from the ultrasound test to prepare for treatments that can be given immediately after birth if necessary.

Serious heart defects usually become evident during the first few days, weeks and months of life. Your child's skin may lose its healthy color and look pale gray or blue. Swelling may develop in the legs, abdomen or areas around the eyes. Perhaps your baby has shortness of breath during feedings, which leads to poor weight gain. Although other conditions can cause such symptoms, they all may be signs of congenital heart defects.

In all, there are more than 35 common congenital heart defects, falling mainly into these categories:

• Holes in the heart. Several defects can be thought of as holes in the walls between heart chambers or abnormal passageways between major blood vessels leaving the heart. These holes allow oxygen-rich and oxygen-poor blood to mix. If the holes are large and a lot of blood is mixed, your baby's skin or the area under the fingernails may be a slight bluish color. He or she may also develop signs and symptoms of congestive heart failure, such as shortness of breath, fatigue and leg swelling, because blood is flooding (overcirculating) the lungs. Examples of hole defects include ventricular septal defect, which is a hole in the wall between the right and left ventricles, and patent ductus arteriosus (DUK-tus ahr-teer-e-O-sus), an opening between the pulmonary artery and the aorta. During fetal development, this opening allows blood in the fetus to bypass the lungs. Within a few hours after birth, however, it should close. If it doesn't, oxygen-rich blood intended for the body is directed back to the lungs.
• Obstructed blood flow. When vessels or valves become narrowed, the heart must work harder to move blood through them. Imagine trying to squeeze water out of a small hole in a balloon, rather than a large hole, and you'll get the idea. Among the most common obstructive defects is pulmonary stenosis (stuh-NO-sis), a narrowing of the pulmonary valve, through which blood passes from the right ventricle to the pulmonary artery. Another obstructive defect, aortic stenosis, is a narrowing of the aortic valve, through which blood passes from the left ventricle into the aorta, eventually causing the heart muscle to thicken and the left ventricle to enlarge.
• Abnormal blood vessels. Several congenital heart defects involve incorrectly formed or positioned blood vessels going to and from the heart. For example, transposition of the great arteries occurs when the pulmonary artery and the aorta are on the wrong sides of the heart. This is a serious and immediately life-threatening defect.
• Heart valve abnormalities. If the heart valves can't open and close correctly, blood can't flow smoothly. Examples include Ebstein's anomaly, in which the tricuspid valve is malformed and often leaks, and pulmonary atresia, in which a solid sheet of tissue forms in place of the pulmonary valve and blocks normal blood flow to the lungs. Both defects prevent oxygen-poor blood from circulating to the lungs.
• A combination of defects. Some congenital heart conditions are the result of not one but several defects. For example, tetralogy of Fallot is a combination of four defects: a hole in the ventricular septum, a narrowed passage between the right ventricle and pulmonary artery, a shift in the connection of the aorta to the heart, and thickened muscle in the right ventricle.

SLIDE SHOW

  Common types of congenital heart defects
 

Most congenital heart defects arise from errors early in the heart's development, so the cause is unknown. But certain environmental and genetic risk factors have been identified. They include:

• German measles (rubella). Your doctor can test you for immunity to this viral disease before pregnancy and vaccinate you against it if you aren't immune. You should wait at least 28 days after being vaccinated before attempting to conceive.
• Diabetes. This chronic condition can interfere with the development of your baby's heart. You can reduce or eliminate the risk by carefully controlling your diabetes before attempting to conceive.
• Medications. Give your doctor a complete list of the medications you take before attempting to become pregnant. Medications that increase risk include the acne drug isotretinoin (Accutane) and lithium (Eskalith), which is used to treat bipolar disorder, a condition that causes intense mood swings. Also avoid alcohol during pregnancy because babies with fetal alcohol syndrome often have congenital heart defects.
• Heredity. Congenital heart defects appear to run in families and are associated with many genetic syndromes. More than one-third of children with Down syndrome — which is caused by an extra 21st chromosome (trisomy 21) — have heart defects. A deletion (missing piece) of genetic material on chromosome 22 also causes heart defects. Genetic testing can detect such disorders during fetal development. Researchers have identified several genes critical for the proper development of the heart. If you already have a child with a congenital heart defect, a genetic counselor can predict the approximate odds that your next child will have one.

A congenital heart defect may have no long-term effect on your child's health — in some instances, such defects can safely go untreated. Sometimes they aren't even discovered until adulthood.

On the other hand, a severe congenital heart defect such as hypoplastic left heart syndrome, in which the left side of the heart is too small to support life, may be fatal shortly after birth. If a child with a severe and complicated heart defect survives infancy, he or she may require close medical supervision and repeated surgical procedures that may include a heart transplant.

Thanks to treatment advances, the odds are improving even for infants with multiple, serious congenital heart defects. Tetralogy of Fallot, once considered lethal, is now usually correctable. In babies with normal birth weight, complete repair in a single operation may be possible. For low birth weight babies, the defect may be partially repaired during an initial surgery and fully corrected during a later operation.

Many children and adults now have their congenital heart defect repaired with a nonsurgical procedure called catheterization. The doctor inserts a thin tube (catheter) into a leg vein and guides it to the heart with the help of X-ray images. Until recently, an atrial septal defect — a hole between the heart's upper two chambers — could only be treated with open-heart surgery. Today, such a hole is usually closed with an expandable disk delivered to the heart by a catheter.

Parents of children with congenital heart defects may worry about the risks of rough play and vigorous activity even after successful treatment. Although some children may need to limit the amount or type of exercise, many can lead normal or near-normal lives. Your doctor can advise you about which activities are safe for your child. If some activities do pose special dangers, encourage your child in other pursuits instead of focusing on what he or she can't do. Although every circumstance is different, remember that most children with congenital heart defects grow up to lead healthy, productive lives.