Certain sounds pertaining to the heart and lungs are heard in all normal persons. These normal sounds vary in quality and intensity for different individuals depending on the physical make-up of the particular organs producing them and also on the structure of bone and flesh through which the sounds are transmitted to the surface of the body. Pathologic changes can often be detected by the modification of the normal sounds or by the appearance of abnormal sounds. In this article, consideration is given to the nature of normal and abnormal heart sounds with a view to presenting preliminary information relative to their quality and frequency characteristics. Sound is a form of vibrational energy. Sounds are created by vibrating bodies of some sort and travel through gases, liquids or solid matter in the form of compressional waves. As these waves progress through a medium they become weakened, partly because their energy