In kidney and liver transplantation, sirolimus therapy has been shown to be comparable to cyclosporine in a head-to-head comparison, but it results in better preservation of renal reserve. In heart transplantation, information about the use of sirolimus is limited. We present the results of the progressive conversion from cyclosporine to sirolimus in a series of 8 heart transplant patients in whom renal dysfunction developed. The baseline creatinine level was 2.4 +/- 0.5 mg/dL, and plasma levels of cyclosporine were within the therapeutic range. After the introduction of sirolimus, the creatinine level fell within the first month to 1.76 +/- 0.2 mg/dL, or mean decrease of 0.6 +/- 0.25 mg/dL (P < .05). After 3 +/- 2.2 months the improvement continued (1.69 +/- 0.2 mg/dL). In 1 patient sirolimus was withdrawn during the first 24 hours, because of gastric intolerance. No patient developed an opportunist infection, allograft rejection, or important hematologic disorder. We conclude that sirolimus appears to be effective in heart transplant patients to improve renal function.