The heart produces mainly four types of sounds [5] in one heart cycle denoted as S1, S2, S3, and S4. The first heart sound (S1, lub) is produced by the atrioventricular valves (i.e., mitral and tricuspid), the second heart sound (S2, dub) is produced by the semilunar valves (i.e., aortic and pulmonary valve)