a method and blood bag , whereby a substantial volume of concentrated whole blood can be quickly and easily recovered from the cardiopulmonary bypass circuit of a patient immediately following cardiac or thoracic vascular surgery . this is achieved in an operating room , by transferring most of the blood in the cpb circuit into a sterile bag located in the surgical field , removing the bag with blood from the surgical field , and outside the surgical field , but preferably in the operating room , hemo - concentrating the blood in the bag , while the bag is fluidly connected to the bypass system hardware . a novel blood bag system is especially adapted for use with the method of the present invention . the new hemo - bag system comprises a closed , sterile bag of substantially transparent , bio - compatible material , defining upper and lower ends . an infusion port is located at the upper end of the bag . an outlet port , an inlet port , and an iv line are situated at the lower end of the bag . a baffle is preferably located inside the bag , for directing upward flow entering the bag through the inlet port , away from the outlet port . each of the ports and line terminate in connector structure , and can be opened or closed by way of conventional clips and caps .