 This study is being conducted to test the hypothesis that coadministration of clopidogrel with DS-1040b will be safe and well tolerated. Subjects entering the study will initially receive a single 12 hour infusion of DS-1040b, to generate data on the effect of DS-1040b alone. After a wash-out period to ensure that no DS-1040b is left in the blood subjects will receive repeated clopidogrel doses over 5 days to generate data on the effect of clopidogrel alone. On the sixth day subjects will receive both DS-1040b and clopidogrel, and the effects will be compared to when the two treatments were given alone. 