Switching From Fondaparinux to Bivalirudin or Unfractionated Heparin in ACS Patients Undergoing PCI

Inclusion Criteria: 1\. The patient is, male or female, \> 18 years of age; 2. The patient presents with coronary syndrome, unstable angina or non ST segment elevated myocardial infarction (NSTEMI) defined as at least one of the following criteria: * Elevated creatine kinase MB or Troponin I or T (above ULN) * ECG changes indicative of ischemia 3. The patient is scheduled for angiography, with possible angioplasty, evaluation of their coronary disease; 4. The patient is able and willing to conform to the requirements of the study and voluntarily signs an Informed Consent. 1. ST elevated myocardial infarction within the preceding 48 hours; 2. Patient weighs more than 400 lbs (181.2 kg) or less than 110 lbs (50 kg); 3. Patients presenting on or received bivalirudin, GP IIb/IIIa inhibitors or low-molecular weight heparin within the preceding 24 hours; 4. Patients that received unfractionated heparin less than or equal to 90 minutes prior to fondaparinux administration. 5. Patients with known conditions of bleeding diathesis or actively bleeding within the previous 6 months (GI bleed etc.); 6. Known diagnosis of acute bacterial endocarditis; 7. Patients with cardiogenic shock or required intra-aortic balloon pump (IABP) 8. If patient is on warfarin (Coumadin) therapy; 9. Patients who had a major or minor stroke (CVA or TIA) or major surgery within the past 6 months; 10. Known impaired renal function (creatinine ≥ 3.0 mg/dL (265.2 μmol/L),) status post renal transplant, patients on chronic dialysis or creatinine clearance ≤ 30 ml/min; 11. A platelet count of less than 100,000 cells/mm3; 12. Known allergies to fondaparinux, aspirin, clopidogrel bisulfate (PlavixR), ticlopidine (TiclidR), heparin, bivalirudin, or contrast that cannot be medically managed; 13. Prior angioplasty within the previous 30 days; 14. Contraindication to low-molecular weight heparin, unfractionated heparin or bivalirudin; 15. Pregnant or lactating women; 16. Any significant medical condition, which in the investigator's opinion, may interfere with the patient's optimal participation in the study; 17. Currently participating in an investigational drug or another device study.