Sepsis resulting from intraoperative transfusion of a contaminated blood product is a rare clinical problem. This case report illustrates the use of a thermodilution catheter to acutely diagnose increased cardiac output and low systemic vascular resistance in a patient with gram negative sepsis resulting from intraoperative transfusion of blood contaminated with Yersinia enterocolitica. The literature relating to Yersinia enterocolitica as a pathogen in banked blood is summarized. The exclusion of donors with a recent diarrheal illness, the discarding of blood older than twenty days, or the interval culturing of such blood needs to be examined closely to evaluate ways to prevent transfusion of blood with significant bacterial contamination.