OBJECTIVE: With the increasing longevity of heart transplant recipients, the long-term effects of cyclosporine on renal function have become more evident. Highly sensitive, early, and effective monitoring of posttransplant renal function is still being researched. This study aimed to evaluate the prognostic value of cystatin C for patients after heart transplantation. METHODS: Seventy-three long-term recipients of a heart transplant more than 5 years before the study start were included in the analysis with a follow-up of 4 years. Serum creatinine, renal glomerular filtration rate calculated by the Modification of Diet in Renal Disease formula, and serum cystatin C levels were collected, and risk factors for renal dysfunction were assessed. Statistical analysis was performed for all patients. RESULTS: Univariate analysis showed a prognostic impact of antihypertensive medication and onset of diabetes (P < .001) on renal failure after transplantation. Multivariate analysis yielded cystatin C measured at the study start as a superior prognostic parameter for all time points (area under the receiver operating characteristic 12 months: 0.963; 24 months: 0.910; 48 months: 0.949) compared with the conventionally used creatinine levels. CONCLUSIONS: Our results showed an enormous potential of serum cystatin C as an early prognostic and easy to obtain biomarker for renal dysfunction after heart transplantation.