Auscultation
Heart sounds, as heard by auscultation, are caused by
movements of the 
heart valves. S1, the first sound,
also called
"lub", is actually two sounds consisting of the closing of
the
mitral and tricuspid valves between the ventricles and atria.
"Lub" marks the beginning of systole. After a brief pause a
second sound, S2 or 
"dub", is produced as the aortic and
pulmonic
valves close together at the end of systole. This is then
followed by another pause during diastole (relaxation). Although
S1 and S2 are usually heard as one sound, pathological conditions
can cause each part to become separated or split from the other
resulting in a split S1 or a split S2.
To best hear the heart sounds, the stethoscope should be
placed in 
specific areas of the chest. The heart is normally
located between the second and sixth intercostal spaces, just
slightly to the left of mid-sternum.
As the heart contracts, it pushes against the chest wall so
that the point of maximal impulse 
(PMI) is at the fifth
intercostal space at the midclavicular line. In the case of
ventricular enlargement, the PMI will be displaced left and
downward.
heart valves. S1, the first sound,
also called
"lub", is actually two sounds consisting of the closing of
the
mitral and tricuspid valves between the ventricles and atria.
"Lub" marks the beginning of systole. After a brief pause a
second sound, S2 or 
"dub", is produced as the aortic and
pulmonic
valves close together at the end of systole. This is then
followed by another pause during diastole (relaxation). Although
S1 and S2 are usually heard as one sound, pathological conditions
can cause each part to become separated or split from the other
resulting in a split S1 or a split S2.
specific areas
(PMI)