The Fontan procedure is the third stage of the repair. It is done when the child is between 18 months and 2 years of age. A heart catheterization is done before the Fontan.
The Fontan is done so that almost all the blue blood coming back from the body goes to the lungs. After this stage, most children are much "pinker" because now nearly all of the blood pumped out to the body goes to the lungs first.
The patch that was placed in the right upper chamber is removed (1).
A wall, called a baffle (2), is built in the right upper chamber. The baffle guides the blue blood coming from the lower body into the blood vessels that go to the lungs (the pulmonary arteries).
A small hole, called a fenestration (3), is made in the baffle. This allows a small amount of blue blood to go across the baffle into the right upper chamber. This hole works like a pop-off valve in case the pressure in the lungs gets too high. The size of the hole may vary. For most children, a small hole is made that will close by itself over time. In some children, a larger hole is needed. Closure of large holes is usually done six to twelve months later during a heart catheterization.