The leading cause of death in the United States and European countries is ischemic heart disease. It has been shown that platelets are involved in the pathogenesis of atherosclerosis and its complication such as myocardial infarction. Regarding the anti-platelet activities of soy components, it is, of course, of considerable importance to identify these compounds in order to develop food supplements with profound anti-platelet activity. Therefore, it was the aim of the present study to identify such molecules predominantly by analysing in vitro aggregation of platelets from healthy volunteers and patients with coronary artery disease (CAD) and/or atrial fibrillation (AF). These analyses were focused on peptides in the absence and presence of isoflavones. Peptides had to fulfil two prerequisites: (i) Molecules had to be frequently found in two proteins of soy bean, i.e. glycinin and β-conglycinin. (ii) They had to consist of no more than three amino acids, since studies on absorption of di- and tripeptides clearly indicated that these molecules are absorbed by intestinal peptide transporters such as PEPT 1. It was shown in the present in vitro study that predominantly acidic peptides such as glutamate-glutamate, aspartate-glutamate, and glutamate-glutamate-glutamate had a major impact on thrombocyte function by enhancing the inhibitory actions of genistein on platelet aggregation of healthy volunteers and CAD patients. Further in vivo studies are warranted to clarify whether bioactive peptides together with genistein are able to reduce platelet aggregability after oral ingestion of these compounds. Not only CAD patients, but especially patients with atrial fibrillation who have chronically activated platelets and suffer under a clearly increased risk of a potentially life threatening apoplexy would have a benefit of digestible molecules which are able to tone down chronic platelet activation.