stethoscope directly over the
valves. Normal heart sounds, Sl (systolic) and S2 (diastolic),
can be auscultated in the positions shown without the patient
disrobing, except to expose the upper chest to the level of the
second intercostal space.
The individual heart valve sounds can be best heard by
placing the diaphragm of the stethoscope directly over the
valves. Normal heart sounds, Sl (systolic) and S2 (diastolic),
can be auscultated in the positions shown without the patient
disrobing, except to expose the upper chest to the level of the
second intercostal space.
Placing the diaphragm of the stethoscope on the first
position, you should hear the familiar 
lub-dub
or Sl and S2
sounds quite clearly. The "lub", or lower pitched sound, is the
Sl
sound representing closure of the tricuspid and mitral valves
at the beginning of systole. 
S2 marks the beginning of diastole.
It is higher pitched and it is louder because the stethoscope
head in this position is closer to the aortic and pulmonary
valves. It is useful to palpate the carotid pulse as you listen
to the "lub-dub" pattern to assure that what you hear as S1
actually coincides with systole.
At this location you should be able to hear single 
crisp S1
and S2 sounds even though mitral valve closure precedes tricuspid
valve closure by 0.02 - 0.04 seconds and the aortic valve closure
precedes pulmonic valve closure by 0.01- 0.07 seconds. Split S1
or S2 sounds must be at least 0.2 seconds wide to be discernible
by the human ear. This also assumes the proper location of the
stethoscope head. The louder sounds of the aortic and mitral
valves, as well as intrathoracic pressure changes during,
breathing can alter the ability to detect the 
Split S1 or S2
sounds. Sl and S2 sounds are usually quite crisp and the splits
are not usually discernible in the adult.
If the diaphragm is moved to the second position shown, the split S2 can be detected during inspiration. The pulmonic valve sound is softer, due to lower pressures in the right heart, making the pulmonic valve sounds only discernible over the pulmonic valve. The aortic valve sound is dominant. A persistent S2 split should be further investigated as it can be a sign of right bundle branch block, atrial septal defect or left bundle branch block, also called paradoxical splitting.
If the heart is auscultated in the apex position the mitral component of S1 is dominant and the tricuspid component is softer. In order to detect the Sl split the diaphragm should be moved closer to the sternum and slightly higher to position.