Objective: To investigate if intra-aortic balloon pump(IABP) is contraindicated without anticoagulation therapy. Methods: Some 153 IABP patients in the King Abdulaziz Cardiac Center(KSA) were randomly assigned into two groups. Anticoagulation group(Group A) consisted of 71 patients who were given heparin intravenously with target aPTT 50-70 seconds. Non-anticoagulation group(Group B) consisted of 82 patients without intravenous heparin during balloon pumping. Hematological parameters including platelet count, D-dimer, Plasminogen activator inhibitor-1(PAI-1) and fibrinogen degradation products(FDP) were checked respectively at the point of baseline, 24 hours, 48 hours and 24 hours post IABP counterpulsation. Clot deposits on balloon surface, vascular complications from IABP including bleeding and limb ischemia were recorded. Results: Platelet count and PAI-1 level decreased at 24 hours and 48 hours in both groups (P0.05). No major limb ischemia in either group. Two patients in Group A suffered major bleeding and required blood transfusion or surgical intervention, whereas no patient had major bleeding in Group B. Eight patients had minor bleeding in Group A, but only 2 patients in Group B(P