CausesBy Mayo Clinic staff
How the heart works
The 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 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
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, the heart begins to bend to the right and fold in on itself to form a loop. By 28 days after conception, 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.
It's usually at this point in your baby's development that heart defects may begin to develop. Researchers aren't sure exactly what causes defects to begin, but they think some medical conditions, medications and genetics 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. Several heart defects can be thought of as holes in the walls between heart chambers or 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, the blood that ends up being circulated through your child's body is not carrying as much oxygen as normal. Not having enough oxygen in the blood can cause your child's skin or fingernails to appear blue in color. Your baby may also develop signs and symptoms of congestive heart failure, such as shortness of breath, irritability and leg swelling, because both oxygen-rich and oxygen-poor blood are 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; atrial septal defect, a hole between the upper heart chambers; and patent ductus arteriosus (DUK-tus ahr-teer-e-OH-sus), an opening between the pulmonary artery and the aorta.
- 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. Among the most common of this type of defect is pulmonary stenosis (stuh-NO-sis), a narrowing of the pulmonary valve, through which blood passes from the right ventricle to the pulmonary artery on its way to the lungs. Another obstructive defect, aortic stenosis, is a narrowing of the aortic valve, through which blood passes from the left ventricle into the aorta to supply blood to all of the body. The narrowed valve forces the heart muscle to work harder, eventually leading to thickening and enlarging of the muscle.
- 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. A condition called coarctation of the aorta is a narrowing of the main blood vessel supplying blood to the body. Coarctation of the aorta causes high blood pressure.
- 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 (which is located between the right atrium and the right ventricle) is malformed and often leaks, and pulmonary atresia, in which a piece of heart tissue blocks normal blood flow to the lungs.
- A combination of defects. Some infants are born with several heart 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.
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