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The following are inclusion and exclusion criteria for enrollment in the study:
Inclusion Criteria:
- Presenting or admitted to hospital with symptoms suspected to represent UA or NSTEMI, i.e., clinical history consistent with new onset, or a worsening pattern of, characteristic ischemic chest pain or ischemic symptoms occurring at rest or with minimal activity (lasting longer than 5 minutes or requiring sublingual nitro-glycerine for relief of the pain).
- Available to be enrolled within 48 hours of the onset of the most recent episode of symptoms.
- Planned coronary angiography, with PCI if indicated, within 72 hours of enrollment where possible.
- At least two of the three following additional criteria:
- Age greater than or equal to 60 years
- Troponin T or I or CK-MB above the upper limit of normal for the local institution;
- Electrocardiogram (ECG) changes compatible with ischemia, i.e., ST depression at least 1 mm in 2 contiguous leads or T wave inversion > 3 mm or any dynamic ST shift or transient ST elevation.
-Written informed consent dated and signed

Exclusion Criteria:
- Age < 21 years.
- Any contraindication to UFH or fondaparinux
- Contraindication for angiography or PCI at baseline
- Subjects requiring urgent (<120 minutes) coronary angiography as characterized by those with:
- refractory or recurrent angina associated with dynamic ST-deviation
- heart failure
- life-threatening arrhythmias
- hemodynamic instability
- Subjects already receiving treatment with enoxaparin (or other LMWH), bivalirudin or UFH for treatment of the qualifying events unless the last administered (intravenous(i.v.) or s.c.) dose was:
- ≥ 8 hours for low molecular weight heparin (LMWH)
- ≥60 minutes for bivalirudin
- ≥90 minutes for unfractionated heparin (UFH)
- Hemorrhagic stroke within the last 12 months.
- Indication for anti-coagulation other than acute coronary syndrome (ACS) during the index hospitalization.
- Pregnancy or women of childbearing potential who are not using an effective method of contraception.
-Co-morbid condition with life expectancy less than 6 months.
- Currently receiving an experimental pharmacological agent.
- Revascularization procedure already performed for the qualifying event.
- Severe renal insufficiency (i.e., estimated creatinine clearance <20 ml/min)

Following angiography and confirmation that the subject is to undergo PCI, the subject must also meet all of the following additional criteria in order to be randomised:
- Subjects will have received at least 1 dose of open-label fondaparinux
- The most recent dose of open-label fondaparinux will not have been more than 24 hours before the start of the PCI procedure.