One out of every 100 infants born in the United States has a congenital (present at birth) heart defect - a problem that occurred as the baby's heart was developing during pregnancy, before the baby is born. Congenital heart defects are the most commonly occurring birth defect.

A baby's heart begins to develop at conception, but is completely formed by 8 weeks into the pregnancy. Congenital heart defects happen during these crucial first 8 weeks of the baby's development. Specific steps must take place in order for the heart to form correctly. Often, congenital heart defects are a result of one of these crucial steps not happening at the right time, leaving a hole where a dividing wall should have formed, or a single blood vessel where two ought to be.

What causes congenital heart defects?
The vast majority of congenital heart defects have no known cause. Mothers will often wonder if something they did during the pregnancy caused the heart problem. In most cases, nothing can be attributed to the heart defect. Some heart diseases in children occur more often in families, so there may be a genetic link to some heart defects. Some heart problems are likely to occur if the mother had a disease while pregnant and was taking medications, such as anti-seizure medicines. However, in 85 to 90 percent of the cases, there is no identifiable reason as to why the heart defect occurred.

• Problems that cause too much blood to pass through the lungs. These defects allow oxygen-rich (red) blood that should be traveling to the body to recirculate through the lungs, causing increased pressure and stress in the lungs. Examples include the following:
  

  • Patent ductus arteriosus (PDA).

  • Atrial septal defect (ASD).

  • Ventricular septal defect (VSD).

  • Atrioventricular canal (AV canal or AVC)
    

• Problems that cause too little blood to pass through the lungs. These defects allow blood that has not been to the lungs to pick up oxygen (and, therefore, is oxygen-poor) to travel to the body. The body does not receive enough oxygen with these heart problems, and the baby will be cyanotic, or "blue." Examples include the following:
  

  • Tricuspid atresia (TA).

  • Pulmonary atresia (PA).

  • Transposition of the great arteries (TGA).

  • Tetralogy of Fallot.
    

• Problems that cause too little blood to travel to the body These defects are a result of underdeveloped chambers of the heart or blockages in blood vessels that prevent the proper amount of blood from traveling to the body to meet its needs. Examples include:
  

  • Coarctation of the aorta.

  • Aortic stenosis.

  • Pulmonary stenosis.

Sometimes, there will be a combination of several heart defects, making for a more complex problem that can fall into several of these categories. A complex combination of heart defects known as hypoplastic left heart syndrome, truncus arteriosis, or total anomalous pulmonary venous return can also occur.

Babies with congenital heart problems are treated by specialists called pediatric cardiologists. These physicians diagnose heart defects and help manage the health of children before and after surgical repair of the heart problem. Specialists who surgically correct heart problems in the operating room are known as pediatric cardiovascular or cardiothoracic surgeons.

Learn more about congenital heart disease.