<Tr> <Td_colspan="2"> Problems playing this file? See media help . </Td> </Tr> <P> Heart sounds are the noises generated by the beating heart and the resultant flow of blood through it . Specifically, the sounds reflect the turbulence created when the heart valves snap shut . In cardiac auscultation, an examiner may use a stethoscope to listen for these unique and distinct sounds that provide important auditory data regarding the condition of the heart . </P> <P> In healthy adults, there are two normal heart sounds, often described as a lub and a dub (or dup), that occur in sequence with each heartbeat . These are the first heart sound (S) and second heart sound (S), produced by the closing of the atrioventricular valves and semilunar valves, respectively . In addition to these normal sounds, a variety of other sounds may be present including heart murmurs, adventitious sounds, and gallop rhythms S and S . </P> <P> Heart murmurs are generated by turbulent flow of blood, which may occur inside or outside the heart . Murmurs may be physiological (benign) or pathological (abnormal). Abnormal murmurs can be caused by stenosis restricting the opening of a heart valve, resulting in turbulence as blood flows through it . Abnormal murmurs may also occur with valvular insufficiency (regurgitation), which allows backflow of blood when the incompetent valve closes with only partial effectiveness . Different murmurs are audible in different parts of the cardiac cycle, depending on the cause of the murmur . </P>

Where does the lub dub sound come from