Procalcitonin (PCT), has been identified as a reliable marker of bacterial infection in critically ill patients. After cardiac surgery, infectious and non infectious inflammatory processes can cause a significant increase in PCT production. At present, literature data seem to confirm that repeated measurements of PCT are a better marker than other parameters, both as prognosis and diagnosis aid. Normal PCT levels are less than 0.1 ng/ml. PCT levels < 2ng/ml can be observed after extracorporeal circulation in case of systemic inflammatory response, in the absente of any post operative complication. However, bacterial infection with organ dysfunction should be suspected when PCT levels are higher 5 ng/ml.