This is a multi-center, randomized, double-blind, placebo-controlled study to determine the safety and tolerability of E5555 in subjects with Acute coronary syndrome (ACS).

INCLUSION CRITERIA:

1. Males or Females, 45 - 80 years of age
2. Presenting with features of non-ST segment elevation ACS (unstable angina or Myocardial infarction without persistent ST elevation). and at least one of the following two criteria on admission: Cardiac enzymes≥ ULN for the local institution OR ECG changes compatible with ischemia
3. Randomisation possible within 24 hours of the onset of the most recent symptomatic episode.

EXCLUSION CRITERIA:

1. History of acquired or congenital bleeding disorder, coagulopathy or platelet disorder, or history of pathological bleeding within the last 6 months
2. History of intracranial bleeding, history of hemorrhagic retinopathy, history of recent ischemic stroke or transient ischemic attack, or known structural cerebral vascular lesion
3. Recent trauma, major surgery, Percutaneous coronary intervention or coronary artery surgery
4. Clinically significant haematological, hepatic or renal abnormalities
5. Patients with some specific ST-segment changes, severe congestive heart failure or uncontrolled cardiac arrhythmias at baseline
6. Recent significant (as determined by the investigator) cardiovascular events