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. 1. Specific Aim 1 will determine the impact of a probiotic on circulating leptin and TMAO levels, conventional risk factors for cardiovascular disease and diabetes (total cholesterol, LDL cholesterol, oxidized LDL, triglycerides, C-reactive protein, serum amyloid A, fibrinogen and adiponectin, glucose-dependent- insulinotropic polypeptide (GIP), glucagon-like-peptide (GLP-1), glucagon, insulin), and their relationship to the intestinal microbiota (15 representative microbial groups) as non conventional risk factors. Several blood samples will be collected to measure biomarkers. Participants will provide periodic stool samples in order to measure gut bacterial biodiversity. Lastly, endothelial cell function (flow mediated dilation) will be measured in order to assess blood vessel function. 2. Specific Aim 2 will determine the impact of a probiotic on metabolites derived from the intestinal microbiota as candidates for non-conventional risk factors of cardiovascular disease. The relationship between metabolites derived from the intestinal microbiota, endothelial cell function and risk factors for cardiovascular disease identified in Specific Aim 1 will be correlated.