An atrial septal defect (ASD) is a hole between the upper chambers of the heart. It lets extra blood flow through the lungs, so symptoms are usually quiet at birth and pick up slowly over years. Easy fatigue is the first clue. Kids tire faster than friends, adults need an afternoon nap, or legs feel heavy after one flight of stairs. Heart racing or skipped beats can pop up. You feel a sudden flutter, thud, or notice your pulse is faster than normal. Frequent colds or chest infections happen because the extra lung blood makes a good highway for viruses.... Learn more