Introduction: Sevoflurane is the most volatile anesthetic used during CPB. In addition to the cardioprotective effect, Sevoflurane also promotes reduction in systemic vascular resistance and also an important role in anesthesia maintenance during surgery, preventing patients awaken in the intraoperative. To avoid the awakening during surgery, assessment of the level of consciousness through the bispectral index (BIS) has been the most common method used by anesthesiologists. During cardiac surgery the most critical moment may be the patient is awaken during the warm up phase of CPB. The monitoring of this phase with the BIS has become efficient as to alert the anesthetist that the patient may be waking up.