Causes

How the heart works

The heart is divided into four hollow chambers, two on the right and two on the left. To pump blood throughout the body, the heart uses its left and right sides for different tasks.

The right side of the heart moves blood to the lungs through vessels called pulmonary arteries. In the lungs, blood picks up oxygen then returns to the heart's left side through the pulmonary veins. The left side of the heart then pumps the blood through the aorta and out to the rest of the body.

How heart defects develop

During the first six weeks of pregnancy, the heart begins taking shape and starts beating. The major blood vessels that run to and from the heart also begin to form during this critical time during gestation.

It's at this point in your baby's development that heart defects may begin to develop. Researchers aren't sure exactly what causes most of these defects, but they think genetics, certain medical conditions, some medications and environmental factors, such as smoking, may play a role.

Types of heart defects

There are many different types of congenital heart defects, falling mainly into these categories:

• Holes in the heart. Holes can form in the walls between heart chambers or between major blood vessels leaving the heart.

  In certain situations, these holes allow oxygen-poor blood to mix with oxygen-rich blood, resulting in less oxygen being carried to your child's body. Depending on the size of the hole, this lack of sufficient oxygen can cause your child's skin or fingernails to appear blue or possibly lead to congestive heart failure.

  A ventricular septal defect is a hole in the wall between the right and left chambers on the lower half of the heart (ventricles). An atrial septal defect occurs when there's a hole between the upper heart chambers (atria).

  Patent ductus arteriosus (PAY-tunt DUK-tus ahr-teer-e-O-sus) is a connection between the pulmonary artery (containing deoxygenated blood) and the aorta (containing oxygenated blood). A complete atrioventricular canal defect is a condition that causes a hole in the center of the heart.

• Obstructed blood flow. When blood vessels or heart valves are narrow because of a heart defect, the heart must work harder to pump blood through them. Eventually, this leads to enlarging of the heart and thickening of the heart muscle. Examples of this type of defect are pulmonary stenosis or aortic stenosis (stuh-NO-sis).

• Abnormal blood vessels. Several congenital heart defects happen when blood vessels going to and from the heart don't form correctly, or they're not positioned the way they're supposed to be.

  A defect called transposition of the great arteries occurs when the pulmonary artery and the aorta are on the wrong sides of the heart.

  A condition called coarctation of the aorta happens when the main blood vessel supplying blood to the body is too narrow. Total anomalous pulmonary venous connection is a defect that occurs when blood vessels from the lungs attach to wrong area of the heart.

• Heart valve abnormalities. If the heart valves can't open and close correctly, blood can't flow smoothly.

  One example of this type of defect is called Ebstein's anomaly. In Ebstein's anomaly, the tricuspid valve — which is located between the right atrium and the right ventricle — is malformed and often leaks.

  Another example is pulmonary atresia, in which the pulmonary valve is missing, causing abnormal blood flow to the lungs.

• An underdeveloped heart. Sometimes, a major portion of the heart fails to develop properly. For example, in hypoplastic left heart syndrome, the left side of the heart hasn't developed enough to effectively pump enough blood to the body.
• A combination of defects. Some infants are born with several heart defects. Tetralogy of Fallot (teh-TRAL-uh-jee of fuh-LOW) is a combination of four defects: a hole in the wall between the heart's ventricles, 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.