Inclusion Criteria1. Informed consent,
2. Patients aged >18
3. Patients with prosthetic(mechanical) heart valve
4. Patients with atrial fibrillation or atrial flutter and a major risk factor (previous TIA or stroke, high blood pressure, diabetes, aged >75, moderate/severe left ventricle dysfunction)
5. Who are receiving long-term oral anticoagulation and require elective non-cardiac surgery or an invasive procedure with reversal of their anticoagulant therapy.
Exclusion Criteria1. Evidence of active bleeding within last 30 days prior to stopping warfarin.
2. Platelet count <100 x 109/L.
3. Spinal or neurosurgery.
4. Life expectancy less than 3 months.
5. Calculated creatinine clearance <30 ml/min
6. Patients requiring cardiac surgery.
7. Multiple prosthetic(mechanical) valves or Starr-Edwards valve or prosthetic(mechanical) valve with a history of stroke or TIA
8. History of heparin induced thrombocytopenia (HIT)