Sometimes the defect is so mild that there are no outward symptoms. In other cases, it's so severe that the newborn becomes ill soon after birth. In still other cases, signs and symptoms occur only in later childhood. In the United States, about 25,000 to 30,000 children are born with a heart defect each year. Most of these children can be helped by surgery even if the defect is severe.
Some heart defects cause obstruction to blood flow.
Therefore, the heart must pump harder and increase the pressure in order to pump blood across the obstruction. In addition, if the heart cannot pump the blood out, the body cannot get enough blood to carry on its normal activities. The obstruction can occur anywhere in the veins, arteries, heart valves, or within the heart itself. This is a defect of the valves which allows blood to flow backwards when it is not supposed to do so. The result is that more blood accumulates in the chamber to which the blood flows backwards, and less blood flows forwards.