The recently established classification of cardio-renal syndrome eventually standardized the nomenclature concerning the interactions between pathology of the heart and kidney. Type 1 cardio-renal syndrome (CRS 1), in which the acute decompensation of the cardiovascular system triggers acute kidney injury (AKI), was found to be associated with poor outcome, especially in the setting of cardiac surgery. Early identification of the onset of AKI is limited on account of the current use of merely functional parameters, such as plasma creatinine concentration. Numerous studies are being performed to identify novel markers of AKI and evaluate their effectiveness. The protein NGAL (neutrophil gelatinase-associated lipocalin) is believed to be a good candidate for a sensitive and early indicator of AKI occurrence.