 Patients who have undergone heart or liver transplantation are usually required to remain on medications, such as Prednisone and Cyclosporine A or Tacrolimus, that prevent the body from rejecting the transplanted organ. These medications may cause bone loss which leads to thinning of the bones osteoporosis and therefore greatly increase the risk of having broken bones fractures after transplantation. Several published studies have shown that 14 to 35 of heart transplant patients develop fractures spine, ribs and hip during the first year after transplantation. We have previously shown that alendronate Fosamax, a drug approved by the FDA for prevention and treatment of postmenopausal osteoporosis and prednisone-induced osteoporosis, prevents bone loss after heart transplantation. We are conducting this study to determine whether a newer drug, zoledronic acid, is as effective as alendronate. 