Objective - Off-pump coronary artery bypass grafting (CABG) is hypothesized to be a safer alternative to conventional on-pump CABG, but the comparative risks and benefits of the procedures for neurological outcomes have not been established by prospective randomized testing. The primary objective of this study is to assess the difference in frequency of new ischemic brain lesions in patients randomized to either on- or off-pump CABG. We will test the hypothesis that off-pump CABG is associated with a smaller proportion of patients with new lesions on MRI post-operatively. Secondary objectives will explore the relationship of other imaging markers, blood markers, and results of cognitive testing to the occurrence of new ischemic lesions, and estimate the relative risk of pre-operative factors. We will also conduct an observational substudy of non-randomized heart surgery patients acquiring complementary data to estimate the relative risk of pre-operative and operative factors for the occurrence of new ischemic lesions.