Acute kidney injury is one of the most frequent and clinically important of all postoperative complications in cardiac surgery. It is estimated that almost half of subjects suffer from a deterioration of kidney function after a cardio-pulmonary by-pass. Renal insufficiency impacts upon the outcome in terms of an increase in postoperative morbidity and mortality, and a decrease in quality of life. Recently, a modified and unified classification of cardio-renal syndrome has been devised, which takes into account bilateral association between the heart and the kidneys. Because acute decompensation in heart function leads to acute kidney damage, therefore cardiac surgery-associated acute kidney injury may be recognised as a type 1 cardio-renal syndrome from a pathophysiological point of view. This paper aims to review the current data on the diagnosis of acute kidney injury and preventive strategies that can be implemented in cardiac surgery perioperative care.