The survival of children who have received heart transplants has greatly improved over the last ten years. One reason for this is better control over rejection. Rejection medications require a delicate balance of enough medicine to work without causing side effects. It is a goal to avoid both rejection and side effects from the anti-rejection medicines. Usually several medicines are used together to prevent rejection. One of these medicines is often Mycophenolic Acid or CellceptThis medicine has been used longer for adults than is has for children. More information is needed on using it for children. The dose is usually determined by the patient's weight or body surface area.