Effect of ARC1779 on Cerebral Microembolism in Patients Undergoing Carotid Endarterectomy

Inclusion Criteria: * Male or female patients; * \>/= 18 to \</= 80 years of age; * Carotid stenosis (either symptomatic or asymptomatic); * Planned carotid endarterectomy; * Female patients must be non-pregnant and willing to use effective, redundant methods of contraception (i.e., for both self and male partner) throughout the study and for at least 30 days after discontinuation of study drug treatment; * Male patients must agree to use a medically acceptable contraceptive (abstinence or use of a condom with spermicide) throughout the study and for at least 30 days after discontinuation of study drug treatment; * All patients must be capable of understanding and complying with the protocol and must have signed the informed consent document. Exclusion Criteria: * Lack of acoustic window allowing TCD recordings; * Unable or unwilling to consent; * Metallic prosthetic cardiac valve; * Recent (\<4 weeks) ischemic stroke involving \>1/3 of the MCA territory; * Any history of hemorrhagic stroke; * Thrombocytopenia; * Coagulopathy; * Trauma or surgery within preceding 30 days; * History of bleeding disorder, gastrointestinal ulcers, or other medical problem associated with an increased risk of bleeding; * Use of warfarin and any chronic antithrombotic therapy other than acetylsalicylic acid and/or dipyridamole; patients previously treated with warfarin are eligible if the drug has been discontinued and the INR prior to randomization has returned to \<1.3; * Use of clopidogrel, unless it has been discontinued at least 5 days prior to randomization; * Fibrinolytic or GPIIb/IIIa inhibitor treatment within the preceding 24 hours.