The aim of the study is to describe the effects of hypertonic saline/hydroxyethylstarch solution in comparison to saline solution for 25 + 25 patients undergoing coronary bypass grafting surgery (CABG) using CPB. The study fluid will be given into the venous reservoir of the CPB circuit after aortic declamping. Primary endpoints are the changes in body weight and extracellular water from baseline to the first postoperative morning.