The left side pumps blood to the rest of the body, delivering the oxygen. If there's an ASD or a VSD, this pressure differential means that some blood flows through the hole from the left to the right side. Because it's receiving so much extra blood, the left side of the heart does more than its normal share of work. It may have a tough time coping with the extra load. This can cause symptoms like fatigue, difficult or rapid breathing, failure to grow normally, or chronic respiratory infections.
Larger holes can lead to heart failure and death.
The severity of these symptoms depends on the size and location of the hole. Sometimes the symptoms appear in newborns. Sometimes they don't appear until much later in life. Each case is different.