1. LUISADA, A. A. 1972, The sounds of the normal heart. (St Louis: W. H. Green).
2. HARRIS, A., SurroN, G., and TOWERS, M. 1976, Physiological and clinical aspects of cardiac auscultation. (London: Medicine Ltd).
3. NOVEY, D. N., PENCAR, M., and STANG, J. M. 1990, The guide to heart sounds: normal and abnormal. (Florida: CRC Press).