Wiggers diagram of various events of a cardiac cycle, including a<unk>  at bottom. Heart sounds result from vibrations created by the closure of the heart valves. There are at least two; the first (S1) is produced when the atrioventricular valves (tricuspid and mitral) close at the beginning of systole and the second (S2) when the aortic valve and pulmonary valve (semilunar valves) close at the end of systole.<unk> hy allows the detection of subaudible sounds and murmurs and makes a permanent record of these events. In contrast, the stethoscope cannot always detect all such sounds or murmurs and provides no record of their occurrence. The ability to quantitate the sounds made by the heart provides information not readily available from more sophisticated tests and provides vital information about the effects of certain drugs on the heart. It is also an effective method for tracking the progress of a patient's disease. Discrete and the packet wavelet transform According to a review by Cherif et al., discrete wavelet transform DWT is better at not affecting S1 or S2 while filtering heart murmurs. Packet wavelet transform affects internal components structure much more than DWT does.
Phonocardiogram
Magnetocardiography
Ballistocardiography
Vectorcardiography
Doppler echocardiography
Cardiac electrophysiology
Impedance cardiography
Electrocochleography