BACKGROUND Acute kidney injury (AKI) is a risk factor for adverse hospital outcomes in recipients of a heart transplantation (HTx). Timely recognition of AKI is crucial for the initiation of proper treatment. We hypothesized that serum or urine biomarkers can predict AKI. MATERIAL AND METHODS In this prospective study we evaluated 117 consecutive patients after HTx. AKI was defined as an increase of the serum creatinine level by ≥50% or a worsening of the renal function requiring renal replacement therapy during the first post-HTx week. We serially sampled serum cystatin C (S-cystatin C) as a marker of glomerular filtration and urinary neutrophil gelatinase-associated lipocalin (U-NGAL) as a marker of tubular damage. RESULTS A cohort of 30 patients (25.6%) fulfilled the criteria of AKI. S-cystatin C allowed the earliest separation between the AKI and non-AKI groups, with a significant difference present as soon as 3 h after surgery and it persisted on days 7, 10, and 30. The increase in S-cystatin C preceded the serum creatinine elevation by 4 days. In a multivariate analysis, S-cystatin C >1.6 mg/L at 3 h after HTx predicted AKI with OR 4.3 (95% CI: 1.6-11.5). U-NGAL was significantly higher at day 3 in the AKI group (p=0.003) and elevated S-cystatin C (≥2.54 mg/L on day 7) could predict 1-year mortality in these HTx recipients. CONCLUSIONS Our study showed that the measurement of S-cystatin C at 3 h after surgery may help to identify patients with high risk for renal complications. A persistent elevation of S-cystatin C also predicts 1-year mortality.