A Study to Evaluate the Effects of YM872 on Stroke Lesion Volume in Acute Stroke Patients

Inclusion Criteria: * Patients who have suffered an acute ischemic stroke and can be evaluated and treatment initiated within 6 hours after the onset of symptoms (Onset is defined as the time that which the patient was last seen in a normal state, or bedtime for unwitnessed strokes occurring during the night). * Patients who have a three dimensionally measurable lesion compatible with an acute ischemic stroke measured using MRI. * Patients who have a National Institutes of Health Stroke Scale (NIHSS) score of at least 7 but not more than 23 and who are conscious. * Patients who are able to provide written informed consent or have consent provided by a legally authorized representative. * Patients who are at least 18 years of age. * Other criteria as specified in the study protocol Exclusion Criteria: * Patients who have received alteplase (t-PA) for the current stroke episode. It is assumed that all patients who are eligible will receive treatment with t-PA. * Patients who have disability and functional limitations prior to the current stroke episode (e.g. deficit resulting from a prior stroke). * Patients who have brain hemorrhage. * Patients who have stroke of the brainstem or cerebellum. * Patients who cannot be evaluated using MRI due to the presence of a pacemaker, claustrophobia, need for sedation, etc. * Patients who have renal (kidney) disease or insufficiency. * Patients who have active epilepsy or convulsions during the current stroke episode. * Patients who are IV drug users or are inebriated. * Patients who have a history of drug-related anaphylaxis. * Patients who have taken sedatives, anticonvulsants, or any medication with sedating effects in the 10 days prior study enrollment. * Patients who have taken more than 1.3 g of aspirin per day in the 2 days prior to enrollment. * Patients who have a known vitamin hypersensitivity. * Other exclusion criteria as specified by the study protocol.