Abstract Background: Despite the availability of newer anticoag-ulants, unfractionated heparin remains a mainstay anticoagulant for atrial fibrillation, acute coronary syndrome with or without percutaneous intervention, treatment and prevention of deep vein thrombosis (DVT), pulmonary embolism (PE), and other thromboembolic disorders. Aim of Study: The aim of this study is to investigate if intravenous heparin dosing based on lean body weight (LBW) of obese patients would be safe and effective in achieving activated partial thromboplastin time (APTT) within 24 hours compared to the usual practice. Patients and Methods: This is a case-control study con-ducted in Cardiology Department Sammanaud General Hos-pital from May 2017 to May 2018 to investigate if intravenous heparin dosing based on LBW of obese patients would be safe and effective in achieving target APTT within 24 hours compared to the usual practice. The study included 50 obese patients with a diagnosis of atrial fibrillation, suspected or confirmed deep venous thrombosis or pulmonary embolism, unstable angina or Non ST elelvation myocardial infarction with hemodynamic stability, or peripheral vascular disease. Patients aged >18 years randomized into two groups (1) and (2). Results: Studies found that unfractionated heparin dosage adjustments based on the patient's LBW provided therapeutic anticoagulation more rapidly and safely, but protocols based on total body weight increase the risk of a supra-therapeutic PTT. Conclusion: Unfractionated heparin remains a mainstay anticoagulant for atrial fibrillation, acute coronary syndrome with or without percutaneous intervention, treatment and prevention of deep vein thrombosis (DVT), pulmonary embo-lism (PE), and other thromboembolic disorders. As lean body weight contributes to approximately 99% of a drug's clearance, it is useful for guiding dosing in obesity. These findings may enhance the utility of LBW as body descriptor instead of TBW in calculating the effective doses of UFH in treatment of thromboembolic disorders.