The changes in respiration and hemodynamics during open heart surgery were studied in 25 patients undergoing coronary artery bypass grafting without blood transfusion. The respiratory and circulatory parameters were measured at the time of anesthetic induction and after cardiopulmonary bypass (CPB). The values after CPB were compared with those at the time of anesthetic induction. The values of HR, CI, SVI and mPAP increased, and the values of mAP, SVRI and PVRI decreased after CPB. The PaO2, BE and pH decreased but PaCO2, A-aDO2 and QS/QT increased after CPB. Although VO2I and DO2I increased after CPB, OER (VO2I/DO2I) was unchanged. Arterial lactate, pyruvate and cortisol levels increased after weaning from CPB. Hemodynamics during open heart surgery without blood transfusion showed hyperdynamic state after CPB. Hypoxia was not evident in the peripheral tissue. This suggests that the depression of the oxygen delivery with hemodilution is compensated by hyperdynamic circulation. Coronary artery bypass grafting without blood transfusion seems to offer no clinical problems.