 It is estimated that approximately 25 of people are resistant to aspirin, or do not respond to its effect. These individuals have a four fold higher risk of a heart attack or stroke compared to those who respond to aspirin. Current tests for determining those who are aspirin resistant are not reliable. This study is assessing the effectiveness of a new assay in determining the rate and time it takes for people who are or are not on aspirin in forming a blood clot. 