Patients undergoing intraaortic balloon pump (IABP) therapy are at risk for developing coagulopathies due to the adverse effects of prolonged exposure of the synthetic surface of the polyurethane balloon to blood components. Hemorrhagic risk has been attributed to a number of factors including thrombocytopenia, vascular injury, and/or platelet degranulation which increase the potential of receiving autogeneic blood transfusions. The present study is a prospective evaluation of coagulation using a viscoelastic monitor (Thrombelastograph--TEG) that measures functional aspects of clot development and stabilization in patients being treated with IABP therapy. Following Institutional Review Board approval, six patients undergoing IABP therapy for hemodynamic instability were enrolled in this study. Blood samples were taken prior to balloon insertion, at 8, 16, 24, 48, 72, and 96 hours on IABP therapy, and 24 hours following the removal of the balloon when applicable. Samples were incubated with heparinase to degrade heparin and TEG profiles were subsequently determined in duplicate. Measured parameters on the TEG included R-time, K-time, maximum amplitude, alpha angle, and lysis at 30 and 60 minutes with calculation of the TEG index. Mortality was 33% following IABP discontinuation. Transfusion of packed red blood cells occurred in 50% of the patients during their balloon pump therapy. Patients demonstrated a significant deviance in fibrinolytic potential from pre-IABP lysis (1.6% +/- 1.8) at both 24 hours (18.8% +/- 22.9) and 48 hours (21.9% +/- 28.5) of therapy (p < 0.05) which returned to baseline shortly after balloon removal. Activation of coagulation factors appeared evident by a steadily increasing alpha angle from pre-IABP data (3.1 +/- 9.2) throughout the duration of therapy and 24 hour recovery (53 +/- 14; p < .005), and by a steadily trending increase in the TEG index pre-IABP (.251 +/- 1.4) to post-IABP (2.6 +/- 1.7; p < 0.05). The results indicate that IABP therapy induces an increase in fibrinolytic potential at 24 to 48 hours of balloon pump therapy with a paradoxical trend toward increased coagulability, potentially predisposing the patient to hemorrhagic risk.