Introduction Asymptomatic internal carotid (ICA) stenosis is one of documented risk factors of perioperative ischemic stroke (IS) in cardiac surgery. There is no strict consensus in benefit of prophylactic carotid endarterectomy (CEA) in asymptomatic ICA stenosis to reduce intraoperative IS. Median somatosensory evoked potentials (SEP) is reliable tool for intraoperative neurophysiological monitoring (IONM) of brain perfusion during CEA. Aim of study Determine safety of median SEP monitoring in intraoperative IS prevention. Material and methods From 1st Jan 2013 to 31st Aug 2014 were enrolled 26 patients (20 males (76.9%), 6 females (23.1%) age range 59–84, average 71.9 ± 6.47 years). All patients underwent cardiosurgical procedure in extracorporal perfusion (EC) with IONM of cerebral perfusion. Inclusion criteria: ICA stenosis ⩾50% on one or more sides, asymptomatic >6 months. Unilateral stenosis was detected in 10 (38.5%), bilateral in 13 (50.0%), occlusion with contralateral stenosis was in 3 patients (11.5%). IONM consisted of median SEP and brainstem auditory evoked potentials (BAEP), near infrared spectroscopy (NIRS) were monitored synchronously. Warning and alarm were always directed at anaesthesiologist or perfusionist. Significant changes were defined as: >50% of N20/P25 amplitude decrease in SEP and/or “V” wave in BAEP and or “V” latency prolongation >1 ms. NIRS decrease ⩽40. Coronary bypass was performed in 22 patients (86.4%), aortic valve replacement in 10 (38.5%), mitral valve replacement in 6 (23.1%). Cardiac compartments were opened in 17 cases (65.4%). Results SEP amplitude decrease was detected in 5 (19.2%). In 4 of them (80%) was asymmetrical relevant to higher grade of ICA stenosis. Mean arterial pressure (MAP) increase was most effective manoeuvre in all cases. Full SEP restoration (>50% baseline amplitude) appeared in 3, partial in remaining 2 patients. Decrease of NIRS was recorded in 4 (15.4%) and always bilateral, symmetrical. Both NIRS and SEP decrease was only marginal, and in 1 case only. BAEP changed nonsignificantly. No new neurological deficit appeared in 25 (96.2%) within 24 h. 1 patient could not be clinically evaluated. 3 patients (11.5%) died within 7 days (1 – ileus, 2 circulation failure). Perioperative IS was not recorded. In all surviving 23 patients neither neurological deficit nor TIA/IS within 3 months period after surgery. Conclusion Intraoperative brain hypoperfusion in SEP was detected in about 19% of cases. MAP elevation caused in SEP restitution. No false negative SEP changes were recorded. No new neurological deficit developed during and after surgery. NIRS changes were neither consistent with SEP changes nor neurological outcome.