After having done research, I understand a lot of the terms used in dealing with this defect, but its much easier when explained in this manner. Taken from a mother who has gone through two o the three surgeries with her daughter...
In HLHS, the left ventricle, which is responsible for pumping oxygenated blood to the body, is underdeveloped. Sometimes it's so small it's basically not even there, other times it is there but not able to perform its function adequately. Normally the right ventricle pumps deoxygenated (blue) blood to the lungs, then it goes back to the left ventricle to be pumped to the body. Since the LV can't do this, in an HLHS patient the heart must be modified. The three-stage surgical procedure reroutes the flow of blood so that blue blood goes straight to the lungs, is oxygenated, and then goes to the heart where the right ventricle pumps it out to the body. Basically the heart is converted to a two-chamber heart. It's a lot to wrap your mind around, but the more you hear it and see drawings of it the more it begins to make sense.The medical field has come a long way in treating HLHS, although it has only been successfully treated for about 20 years. The oldest living HLHS patients are now in their early 20s. I know lots of people with HLHS babies/children, and the positive outcomes outweigh the negative. Here are some links to sites I've found to be helpful: