Basic Heart Sounds
The two major sounds heard in the normal heart sound like “lub dub”. The “ lub” is the first heart sound, commonly termed S1, and is caused by turbulence caused by the closure of mitral and tricuspid valves at the start of systole. The second sound,” dub” or S2, is caused by the closure of aortic and pulmonic valves, marking the end of systole. Thus the time period elapsing between the first heart sound and second sound defines systole (ventricular ejection) and the time between the second sound and the following first sound defines diastole (ventricular filling).
There is also a third and a fourth heart sound, S3 and
S4. They can occur in normal persons or be associated with pathological
processes. Because of their cadence or rhythmic timing S3 and S4 are
called gallops. Gallops are low frequency sounds that are associated
with diastolic filling.
The gallop associated with early diastolic filling is the S3 and may be heard pathologically in such states as volume overload and left ventricular systolic dysfunction. The S4 is a late diastolic sound and may be heard in such pathologic states as uncontrolled hypertension.
A common aid in distinguishing these sounds auditorily, is to remember that S3 has the same cadence as the word "Kentucky" and S4 sounds like "Tennessee".