It has been demonstrated that intracardiac phonocardiography provides precise localization of the source of cardiovascular sounds. Can this technic be of practical help in the diagnosis of small or complicated ventricular septal defects? Is a ventricular septal1 defect ever silent? What mechanisiims are responsible for the diastolic mlurmlurs in ventricular septal defect? In an attempt to answer these problemus, intracardiac phonocardiograms have been studied in 47 cases.