I thought I'd show you a diagram of a normal heart. If you really look at it, it describes very well the functions of a normal heart.
Besides my kid's drawings, which I love, I have come to depend upon a few drawings from our baby's Cardiologist. Since I am a very visual learner, the drawings mean more to me than hours of explanation. So, stay with me as I expain things to you.
Specifically, these simple drawings are not based on the structure of a normal heart, but our baby's heart. For our baby, the bottom chamber of the heart, his right ventricle, did not form at all. There is the tiniest hint that it wanted to start developing, but never did. Coming off that ventricle is the Pulmonary Valve. It should have a nice valve that opens and closes, allowing for one-way blood flow from the lower ventricle to the lungs. The muscle of the ventricle, in theory, should be taking that low-oxygenated blood that just finished circulating through the body, and pump it through that valve, up through the artery, and into the lungs so that it can get oxygenated.
From there, the blood that is now high in oxygen, comes back into the heart on the left side, goes down into the left ventricle, where it is then pumped to the body to oxygenate everything.
So with his right ventricle missing, and an essential valve not working, how will our baby get oxygen throughout his body? As you see in the next picture, there are two openings that are vital in keeping our baby alive. The first is an opening between the two top chambers (or atriums) of the heart. This allows the blue blood (low oxygenated blood) to mix with the red blood (high oxygenated blood). Normally this is so minimal, because of the low pressure/high pressure system, that it doesn't make much of a difference. However, because in our baby, the blue blood has no other place to go, because of the missing right ventricle, the blue blood gets pushed over to the left ventricle, and is then pumped back through the body. This means that although blood is getting pumped through the body, it is constantly getting blood without oxygen in it. Without treatment, the baby cannot live much longer than a few days.
The next opening is something called the Patent Ductus Arteriosus (PDA). This is an opening that is present at birth, but normally closes within the first day or two of a newborn's life. It is an opening between the pulmonary artery (the part in our baby that is a closed off valve that tried to connect to the right ventricle) and the aorta. A small amount of oxygenated blood from the lungs actually comes through that aorta, and because that PDA is still open, some of that oxygenated blood is able to get into the left atrium, thus mixing with the low oxygenated blood, and getting pumped through the body.
It is imperative that the PDA stays open, so immediately after our baby is born, he will be put on medication called Prostaglandin (PGE), which will tell the body to keep it open. Because this won't stay open forever, within a day or two, the baby will have his first open-heart surgery. In this surgery, the Doctors will place a shunt to replace the PDA, thus keeping a way for the heart to receive some of the oxygenated blood from the lungs. Although the body will still get a lot of blue blood, he will get enough red blood to maintain some degree of health. This will be surgery number 1.
Surgeries number 2 and 3 will happen around the time he is 4-6 months old, and 2 years old. These procedures are called the Glenn and Fontan procedures. In steps, the arteries are re-routed to bypass the right atrium and ventricle of the heart. Instead, the blood will finish it's cycle through the body and go directly to the lungs to get oxygenated. From there, it will come back into the left atrium and ventricle to get pumped to the body.
As cautioned, the success of these surgeries depend on the size and strength of his pulmonary arteries, to see if they can withstand the extra burden, as well as how strong the left ventricle is, and whether operating on a one-pump system (instead of a two pump system) can be managed to give our baby as normal a life as possible. Without unforeseen complications or other areas of defects, the success rate is about 75%.Hopefully this was a good update for you. I'm sure the heart functions at a much more complicated level than what I understand, but this was how it was explained to me.