The purpose of this study is to determine which short-acting blood thinner (low-molecular-weight heparin [Enoxaparin] or unfractionated heparin) is associated with less discomfort and bruising when given as a subcutaneous (under the skin) injection before and after a planned surgery or procedure in patients who temporarily stop warfarin.

Increasing Patient Comfort and Compliance: The Bridging Anticoagulation Clinic strives to provide the highest quality of care to patients who require temporary interruption of warfarin therapy. An important component of optimizing patient care is minimizing patient discomfort with perioperative administration of short-acting anticoagulants (LWMH or UFH) used for bridging therapy, which, in turn, may optimize patient compliance with this treatment. This issue is especially relevant for patients who are receiving out-of-hospital treatment with LMWH or UFH because about 85% of such patients will be taught to self-administer this medication. This study seeks to determine if there is less discomfort and bruising associated with self-injection of LMWH than with UFH.

Minimizing Injection Site Bruising: No studies, to our knowledge, have assessed the characteristics or clinical importance of bruising in patients receiving subcutaneous LMWH or UFH. Thus, there is no evidence to support any association between bruising and discomfort. To bridge this gap in knowledge, we will document each injection site during the course of the study and measure the amount of bruising observed using a standardized photographic methodology. Injection site bruising has the potential to cause medical problems if an injection site hematoma develops, which can become infected or can cause long-term discomfort.

Inclusion Criteria:

1. Patient is receiving warfarin therapy with a target international normalized ratio (INR) of 2.0-3.5
2. Patient requires temporary interruption of warfarin because of elective surgery or procedure.

Exclusion Criteria:

1. History of allergy to heparin, including heparin-induced thrombocytopenia (HIT)
2. Bridging anticoagulation with low molecular weight heparin (LMWH) or unfractionated heparin (UFH) not indicated
3. Impaired cognitive function or language barrier
4. Creatinine clearance < 30 ml/min
5. Patient declines consent
6. Patient is < 18 years of age.
7. Patient is not willing and able to self inject.
8. Patient has significant visual or hand motor impairment