This trial is a multicenter, randomized, double-blind, placebo-controlled, single dose study initiated prehospital in the ambulance. It is being conducted using Emergency Medical Services (EMS) in Canada. Subjects with suspected acute stroke will be identified in the field by trained paramedics using the approved stroke protocol in use by the local EMS system, and further screened for eligibility and approval by an on-call trial physician. The paramedics will administer the study drug. Upon arrival at the emergency department, subjects will receive standard-of-care.