The aim of the work was to study the O2-transport changes to tissues in cardio-surgical patients suffering from CAD and operated during extra-corporeal blood circulation (ECC). The changes of selected haematologic variables, 2,3-diphosphoglycerate (2,3-DPG) and ATP concentration, acid-base balance parameters with p50 calculation were measured in the venous blood samples taken before the operation, during the operation and on the 1st, 2nd, 3d, 5th, 7th and 10th day after the operation. From the obtained results follows, that extreme haemodilution causes significant decrease of the haematocrit value (Htc) by 35%, the value of haemoglobin (Hb) by 37% and the count of erythrocytes (Er) by 37% from the initial values. The count of reticulocytes (Ret) was increased by 52%. In the days after operation the increase in Htc values, the values of Hb and count of erythrocytes was observed, whereby the initial values were not reach even on the 10th day after the operation. The increase of the reticulocytes count by 33% prevailed to the 10th day after the operation in comparison with the initial values. 2,3-DPG concentration was increased between 3d and 10th day after the operation by 30% and ATP concentration between 5th and 10th day was increased by 23% from the initial values. Hb-O2 saturation (SpO2) and pO2 were increased already during the operation, the increase prevailed until the 7th day by 27%, pO2 until the 3d day by 39% from the initial values. Calculated values p50 did not change in the course of this study--they fluctuated in range +/- 0.04 kPa from the initial value 3.55 kPa. Supposing multifactorial character of Hb oxygenation and deoxygenation process it is possible to conclude, that the determined changes of observed parameters did not significantly influence O2-transport to tissues during ECC. (Fig. 3, Ref. 12.)