Thirty cases of atrial septal defect proved by cardiac catheterization, surgery, or postmorten examination have been investigated with the technic of intracardiac phonocardiography, which provided precise localization of the source of heart sounds and murmurs. The site and mechanism of origin of the many auscultatory signs in uncomplicated atrial septal defect and in cases of Lutembacher's syndrome, tricuspid atresia, and persistent atrioventricular canal were elucidated by direct intracardiac sound recordings and simultaneous external chest phonocardiograms.THERE have been many recent reports of the auscultatory features of atrial septal defect and these have been reviewed both clinically and with the aid of chest phonocardiography.1-7The commonest auscultatory findings in uncomplicated atrial septal defect are a basal systolic ejection murmur, usually soft, and a wide, fixed splitting of the second sound over the pulmonary area. Less frequently an early blowing diastolic murmur is heard at the base and along the left sternal border iii the second and third left intercostal spaces. At the apex, or medial to it, systolic and diastolic murmurs may occasionally be present, together with an accentuated first sound. The systolic apical murmur is usually of regurgitant type (pansystolic) ; the diastolic apical murmur occurs in mid-diastole or inpresystole.There appears to be no general agreement about the site and mechanism of production of these signs. The relative importance of various factors such as the flow across the atrial septal defect, the increased flow through the tricuspid and pulmonary valves, and the From the

No abstract