The purpose of this report is to review the previous and current methods for the detection of a MB and to summarize results of work by other investigators as well as our own recent morphological studies with emphasis on work since 1983. We will discuss the presumable association of MBs with heart disorders, on the basis of significant publications. We describe the importance of both basic and clinical research for the assessment of MB influence in various heart disorders. Aspects covered are: (1) historical background of MBs and the relationship between the MB and CA; (2) general characteristics of MBs; (3) methods for studying MBs; (4) compressive effect of the MB on the CA; (5) clinical symptoms including myocardial ischemia, angina pectoris, myocardial infarction, development of atherosclerosis and thrombosis, ventricular fibrillation and sudden death; (6) treatment of MB-associated heart disorders by resection of MBs and (7) future research trends.