Thromboxane Receptor Antagonist to Improve Endothelial Function

Inclusion Criteria: * Males and females 18-80 years of age with established cardiovascular disease * Take \>=81 mg daily of aspirin as part of their daily medical regimen * Urine thromboxane B2 metabolites \>1145 pg/mg creatinine on screening. * Able to provide written consent and comply with protocol-specific procedures. Exclusion Criteria: * Chronic oral anticoagulation with a non-vitamin K antagonist. * Anticipated change or interruption in aspirin therapy during the study period. * ST segment myocardial infarction within the past 30 days. * Cardiac surgery within the past 30 days. * Stage 4-5 renal failure or on renal replacement therapy. * An ongoing uncontrolled severe inflammatory condition. * Pregnant,intending to become pregnant or breast feeding. * Known ifetroban or aspirin sensitivity Inability to perform vascular testing. * Participation in another investigational drug trial within 30 days of randomization.