['The causes for cognitive impairment after coronary artery bypass grafting (CABG) have long been a topic for debate.', 'We prospectively followed 308 consecutive, unselected survivors of CABG at our institution. In addition to determination of clinical measurements, cognitive brain function was measured objectively by P300 auditory-evoked potentials before CABG, at 7-day and at 4-month follow-up. Standard psychometric tests (Trail Making Test A, Mini Mental State Examination) were also performed.', 'At 7-day follow-up cognitive P300 auditory-evoked potentials were significantly impaired compared with preoperative levels (peak latencies: 376 +/- 40 ms versus 366 +/- 37 ms, p = 0.0001). P300 measurements were almost normalized at 4-month follow-up (peak latencies: 369 +/- 33 ms, p = NS versus preoperative). Standard psychometric tests failed to detect this subclinical cognitive impairment. Multiple regression analysis revealed that use of cardiopulmonary bypass was the only independent predictor of impaired cognitive brain function at 7-day (p < 0.0001) and 4-month follow-up (p = 0.0008). The presence of diabetes mellitus (p = 0.0135) or concomitant repair of significant carotid artery stenosis (p = 0.0049) was predictive of late improvement of cognitive brain function at 4-month follow-up.'] Does cardiopulmonary bypass affect cognitive brain function after coronary artery bypass grafting?