Ventricular septal defect (VSD), the most common heart problem that develops before birth (congenital), is an opening in the wall that separates the lower chambers of the heart. Most ventricular septal defects are small and do not cause a problem.

The opening of a ventricular septal defect can be as small as a pinhole, or the wall between the heart chambers may be completely missing. This defect is usually found when a baby is 1 to 4 weeks old.

A large, untreated ventricular septal defect may result in the lower left heart chamber's inability to pump enough blood to the body and too much blood going to the lungs. Large ventricular septal defects usually cause heart problems and symptoms by the time a baby is 3 to 6 months old.

Treatment is not needed in cases where a ventricular septal defect is small or closes on its own. Some children and adults need surgery or a catheter procedure to close the defect, especially if it is large.