The primary purpose of this study is to demonstrate that a continuous infusion of intravenous (IV) heparin (UFH) for Venous thromboembolism (VTE) prophylaxis will restore prophylactic levels of heparin in high-risk critically ill medical patients as compared with guideline recommended subcutaneous heparin. Antifactor Xa assay, a laboratory test to measure the anticoagulant activity of heparin, or the ability of heparin to thin the blood, will be used to demonstrate that Intravenous administration is more effective.

Inclusion Criteria:

• Admission to the medical ICU (MICU)
• High-risk for Venous Thromboembolism (VTE) ≥ 1 of the following:
• Body Mass Index (BMI) ≥ 30 kg/m2
• Personal or family history of VTE
• Receiving vasopressors

Exclusion Criteria:

• Indication for therapeutic anticoagulation
• Evidence of deep vein thrombosis (DVT) on ultrasonography at admission
• Indwelling intrathecal, epidural, or other indwelling deep catheters
• Recent (< 3 months) International Society of Thrombosis and Haemostasis (ISTH) major bleeding13
• Recent (< 3 months) major trauma
• Recent (< 3 months) neurosurgery or orthopedic surgery Pregnancy
• Contraindication to heparin or heparin products