S3 and S4 sounds
In addition to S1 and S2, third (S3) and a fourth heart sound (S4) may be present. S3 and S4 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, lower than both S1 and S2. It is best to listen to gallops with the bell of the stethoscope resting lightly on the skin. Pressing firmly with the bell often reduces transmission of gallops to below the hearing threshold.
The gallop associated with early diastolic filling is the S3 gallop. S3 occurs 0.13 to 0.18 seconds after S2. This is an example of S3:
Normal or innocent S3 can be heard in many children and some adults. An innocent S3 usually waxes and wanes. S3 may disappear when the patient sits up. A pathologic S3 is usually higher pitched and louder than an innocent S3. It is also more constant than an innocent waxing and waning S3. S3 may be heard pathologically in such states as volume overload and left ventricular systolic dysfunction.
The S4 is a late diastolic sound associated with atrial contraction. S4 may be innocent or may be associated with such pathologic states as uncontrolled hypertension. This is an example of S4:
A common aid in distinguishing S3 and S4 is to remember that S3 has the same cadence as the word "Kentucky" ("Ken-tu-cky" = S1-S2-S3) and S4 sounds like "Tennessee" ("Ten-nes-see" = S1-S2-S4).