A problem with the structure of the heart. It is present at birth and is the most common type of major birth defect. A baby's heart develops while in the womb and structural defects can occur during this time. These heart defects can involve any portion of the heart including the walls of the heart, the valves of the heart and the arteries and veins of the heart. The defects can disrupt the normal flow of blood through the heart, and prevent the baby from getting enough oxygen. Babies may not show signs of these problems immediately after birth but can begin having symptoms they go home from the hospital. Some heart defects can be very serious and even result in death.