Early initiation of heparin therapy for treatment of stroke is not only associated with an improved outcome, but also with the risk of hemorrhagic transformation. We compared the efficacy of three unfractionated heparin bolus regimens (0 U/kg, 30 U/kg, or 80 U/kg) in achieving a therapeutic activated partial thromboplastin time over the first 6-hour period in a cohort of 54 patients admitted with transient ischemic attack or stroke. Patients treated with the low bolus dose (30 U/kg) were more often within the therapeutic range for activated partial thromboplastin time at two hours after the initial bolus than patients treated with the other regimens. The percentage of therapeutic activated partial thromboplastin time results within the first six hours of treatment was greater in the group treated with the low bolus dose. Using the low bolus dose may reduce complication rates and improve clinical outcomes in the future clinical trials.