It is standard treatment to take anti-platelet medication after cardiac catheterization and stent placement to help prevent the formation of blood clots that may cause heart attack or stroke. The most commonly used anti-platelet medicine is clopidogrel (Plavix®). However, researchers have found that people vary in their response to clopidogrel, in part because of differences in their genes. Prasugrel (Effient®)is another anti-platelet medication used to prevent clots. The genetic differences that affect clopidogrel response do not affect prasugrel response. Recently, the FDA added a warning to the label of clopidogrel to notify doctors and patients with certain genetic differences may not get the full benefit from clopidogrel. Despite this, genetic testing for these variations is not usually done in standard medical practice. The purpose of this study is to see if patients with certain gene differences have fewer major cardiac events after stent placement if they are given anti-platelet therapy guided by their individual genetic type compared to standard anti-platelet therapy.