Preliminary studies have shown that people with diabetes who undergo heart surgery may have a higher risk of developing cognitive functioning problems, including memory problems, than people without diabetes who undergo heart surgery. Among people with diabetes, however, those who control their blood sugar levels in a more intensive way during and after heart surgery may have better neurological outcomes than those who use a standard method of controlling their blood sugar levels. This study will compare the effectiveness of using a traditional method of blood sugar control versus a more intensive method of blood sugar control during and after heart surgery for improving neurological outcomes in people with diabetes.