This study will examine the effect of supplemental magnesium on the neurocognitive function of individuals undergoing CABG surgery. The two hypotheses to be tested include the following: 1) therapeutic levels of magnesium reduce post-operative neurocognitive dysfunction after heart surgery; and 2) therapeutic magnesium levels protect quality of life through reduced cognitive dysfunction after heart surgery. This double-blind study will enroll 400 individuals and randomly assign them to either the treatment group, which will receive 100 mg/kg of magnesium, or to the control group. Anesthesia management will be standardized to minimize any impact that anesthesia may have on neurologic or neuropsychologic outcome. Neurocognitive testing will be conducted prior to surgery, and 6 weeks and 1 year following surgery.