This paper presents quantitative heart sound analysis, based on which the Heart Sound Information System (HSIS) has been built. Heart sound analysis provides important information of cardiovascular diseases so it has been a basic requirement for every doctor and medical student. We use objective measurement and analysis in terms of physiology and pathology of heart sound and approaches of knowledge engineering to recognize and classify the heart sound waveform automatically or semi-automatically, so that we can get useful data to aid in clinical diagnosis. The basic points for heart sound quantitative analysis are: (1) the mean amplitude of white noise is abstracted and used as the waveform baseline; (2) measuring the duration for each component of heart sound (first heart sound, second heart sound, etc.); (3) indicators are produced based on the data from above, which is needed for heart sound diagnosis. HSIS has been tested using real heart sound samples.