Researchers at MCW have discovered a new pathway that links the type of bacteria present in the intestines to the severity of heart attacks. This discovery of a relationship between intestinal bacteria, bacterial metabolites, and severity of heart attacks means that for the first time, the investigators may be able to determine a person's probability of having a heart attack via non-conventional risk factors. This may provide opportunities for novel diagnostic tests as well as a potential for therapeutic intervention. The link between gut microbiota and the severity of heart attacks may also lead to novel therapeutic approaches (probiotics, non-absorbable antibiotics) to prevent heart attacks from happening. The studies proposed will test the hypothesis that altered intestinal microbiota are mechanistically linked to the pathogenesis of cardiovascular disease. The investigator's objective is to determine whether inflammatory markers in the blood are decreased and endothelial cell function improved by a probiotic in patients with established coronary artery disease. Furthermore, the investigators wish to elucidate a mechanism by which the gut microbiota regulates serum inflammatory markers.