Small defects in the walls of the heart can often be heard as loud, harsh murmurs in a baby's heart when he or she is several months old. Larger ones can be heard when the baby is only two to three weeks old. By the time the baby is six to eight weeks old, signs of heart failure may appear as flooding of the lungs occurs.
Babies with significant defects or who are in heart failure that has not been stabilized are at a high risk of getting pneumonia and needing mechanical breathing support. The baby's heart may become enlarged. The baby may fail to grow or may develop endocarditis.