The purpose of this study is to compare different types of rehabilitation after coronary bypass surgery. The investigators wish to compare rehabilitation in an institution for four weeks with a home based rehabilitation. They also wish to compare rehabilitation in an institution for four weeks with a rehabilitation program were the patients live at home but visit the hospital twice a week for twelve week. The investigators will measure the patients' physical capacity by measuring their maximal oxygen consumption. The investigators will also analyze their blood and their endothelian function (how well their arteries dilate).