["The plasma protein apolipoprotein E (APOE) is a risk factor for degenerative cognitive decline manifested by mild cognitive impairment and later by Alzheimer's disease. Patients undergoing coronary artery bypass grafting (CABG) are known to have a high prevalence of preexisting cognitive impairment and postoperative cognitive dysfunction. Because both mild cognitive impairment and Alzheimer's disease generally occur in elderly individuals, the age group that commonly present for CABG, we investigated if the APOE epsilon4 allele was associated with patients manifesting preexisting cognitive impairment and postoperative cognitive dysfunction.", 'The DNA of 282 patients who had undergone neuropsychologic testing before and 3 and 12 months after CABG was analyzed for APOE genotype. Patients were classified as having preexisting cognitive impairment if cognitive function was decreased in two or more tests compared with a healthy control group. Postoperative cognitive dysfunction was defined as a decrease in two or more tests compared with the group mean baseline score.', 'The APOE epsilon4 allele was found in 83 (29.4%) patients. Although preexisting cognitive impairment was present in 105 (37.2%) and postoperative cognitive dysfunction in 33 (12%) and 31 (11%) at 3 and 12 months postoperatively, there was no relationship with the presence of the APOE epsilon4 allele or any of the six genotypes.'] Is the apolipoprotein E epsilon4 allele associated with cognitive dysfunction in cardiac surgery?