Transplant-associated coronary artery disease (TxCAD) appears to be initiated by endothelial cell activation and inflammation involving inflammatory cytokines and chemokines. Osteoprotegerin (OPG) and receptor activator of nuclear Factor-kappaB ligand (RANKL) have been implicated in cardiovascular disease progression and we measured the expression of these mediators in serum and myocardial biopsies taken serially during the first year after heart transplantation (HTx), relating them to the development of TxCAD. Serum OPG as well as myocardial gene expression of RANK and OPG, but not RANKL, were highest early after HTx and declined progressively. Importantly, patients who develop TxCAD or experience episodes of acute rejection showed a lower myocardial RANKL expression throughout the first year after transplantation than patients without these complications. Our findings may suggest an unrecognized role RANKL in maintaining myocardial and/or endothelial integrity and suggest that RANKL should be further investigated as a parameter that may predict development of TxCAD.