Background: Despite large interpatient variability in dose response, heparin is utilized for treatment of venous thromboembolism (VTE). Current data on the optimal heparin dosing in obese patients are conflicting. Objective: The objective was to evaluate the time and dose required to achieve a therapeutic activated partial thromboplastin time (aPTT) in nonobese, obese, and severely obese patients using a pharmacist-directed heparin dosing protocol. Methods: This was a retrospective cohort study in a single-center community hospital inpatient setting. Adult patients receiving heparin for VTE treatment from July 1, 2013, to July 31, 2015, were evaluated. Patients were categorized into 3 groups: nonobese (BMI < 30 kg/m2), obese (BMI = 30-39.9 kg/m2), and severely obese (BMI ≥ 40 kg/m2). Data on height, weight, initial bolus dose, initial infusion rate, time to therapeutic aPTT, and therapeutic infusion rate were collected. Dosing body weight (DBW) was utilized for patients 20% over their ideal body weight (IBW). The primary outcome was time to therapeutic aPTT. Results: Analysis included 298 patients. Median times to therapeutic aPTT (hours:minutes) in the nonobese, obese, and severely obese were 15:00 (interquartile range [IQR] = 8:05-23:21), 15:40 (IQR = 9:22-25:10), and 15:22 (IQR = 7.54-23:40), respectively (P = 0.506). There was no difference in bleeding among the nonobese (14%), obese (13.9%), or severely obese groups (7.9%; P = 0.453). No adverse thrombotic events occurred during hospitalization. Conclusion: Using a DBW for heparin dosing in patients 20% over their IBW resulted in similar times to therapeutic aPTT and adverse events in the nonobese, obese, and severely obese.