The benefit of a high dose glucose-insulin-potassium (33% glucose, 80 mmol KCl, 120 units of insulin - 1 mL/kg) (GIK) with cardiopulmonary bypass support (CPB) prior to cardioplegic arrest in open-heart surgery has been evaluated in this article. Twenty non-diabetic patients (PTS) were selected upon their preoperatively impaired left ventricular ejection fraction (LVEF < 45%) and were divided into two groups. Group 1 was given GIK and 20 minutes of CPB prior to cardioplegic arrest; Group 2 was the control group with no GIK and no CPB support. Hemodynamics was measured prior to surgery, 30 minutes after weaning from CPB, and 12 and 24 hours postoperatively. There were less rhythm disturbances and need for intraoperative defibrillation in Group 1 (2:10 pts VS 8:10 pts in the Group 2). There were significantly higher values of cardiac index (CI) in Group 1 30 minutes after weaning from CPB (2.5 +/- 0.28 VS 2.11 +/- 0.25: p < 0.01), while there was no significant difference in late postoperative course. Left ventricular stroke work index (LVSWI) in Group 2 was significantly higher 12 hours after the surgery (38.35 +/- 8.93 VS 29.76 +/- 8.17:p < 0.05). At 30 minutes and 24 hours postoperatively there was no significant difference, but clinical difference was observed, probably due to necessary inotropic stimulation in Group 2. There was neither clinical nor statistical difference in right ventricular stroke work index (RVSWI) throughout the whole measurement. The authors emphasise the importance of GIK with CPB in myocardial protection in patients undergoing open-heart surgery.