Congenital heart defects.

Congenital Heart Defects

A congenital heart defect occurs when the heart or blood vessels near it fail to develop normally before birth. Congenital heart defects are present in about one percent of live births and are the most frequent congenital malformations in newborns. In most cases, scientists don't know why they occur. Sometimes, a viral infection causes serious problems. German measles (also called rubella) is an example. If a mother contracts German measles during pregnancy, it can interfere with the development of the baby's heart or produce other malformations.

Certain conditions affecting multiple organs, such as Down's syndrome, can involve the heart. A high number of congenital heart defects result from mothers' drinking too much alcohol or using drugs such as cocaine during pregnancy.

Most heart defects either obstruct blood flow in the heart or vessels near it or cause blood to flow through the heart in an abnormal pattern. An obstruction is a narrowing that partially or completely blocks the flow of blood. Obstructions (stenoses) can occur in valves, arteries, or veins.

The three most common forms of obstructed blood flow are pulmonary valve stenosis, aortic valve stenosis, and coarctation of the aorta. in pulmonary stenosis, the pulmonary valve (which lets blood flow from the right ventricle to the lungs) is narrowed. As a result, the right ventricle must pump harder than normal to overcome the obstruction.

In aortic stenosis, the aortic valve (between the left ventricle and the aorta) is narrowed. This makes it hard for the heart to pump blood to the body.

In coarctation of the aorta, the aorta is pinched or constricted. This obstructs blood flow to the lower part of the body and increases blood pressure above the constriction.

When a baby is born with an opening or defect between the wall the walls separating the sides of the heart, it allows blood to flow between the right and left chambers.

The two most common types of such openings are atrial septal defect and ventricular septal defect. In atrial septal defect, an opening exists between the two upper chambers of the heart. This allows some blood from the left atrium (blood that already has been to the lungs) to return via the hole to the right atrium instead of flowing through the left ventricle, out the aorta, and to the body. In ventricular septal defect, an opening exists between the two lower chambers of the heart. Some blood that has returned from the lungs and...