Design - The study has a prospective randomized single blinded design. Patients will be randomized to on- or off-pump surgical technique if they meet all eligibility criteria. Analyses will be performed blinded to the surgical group assignment and based on intention-to-treat principle. MRI evaluation will be performed prior to surgery, 48 hours after surgery, 30 days and 6 months after surgery. Biomarkers will be quantified in blood drawn before and immediately after surgery and 6, 24, 48 and 72 hours post-operatively. Cognitive testing will also be performed 30 days and 6 months after surgery. Interim analysis after each 20 patients will be performed up to the first 100 patients, with stopping rules if a highly significant difference is observed on the primary outcome variable. Patients randomized but who have no post-operative scan and have no clinical evidence of post-operative stroke will not be included in the sample for the primary analysis. Patients in the observational substudy will undergo the same pre- and post-operative evaluations as patients in the RCT.