Definition
- Heart sounds are produced by vibrations set up by closure of the cardiac valves and by turbulence of blood flow during the cardiac cycle.
- There are four heart sounds, S1 to S4; only S1 and S2 are heard normally.
Normal Characters of the Heart Sounds
Normal characters of the heart sounds
Sound
S1 ('lub')
- Duration
- 0.15 sec
- Frequency / pitch
- 25 to 45 Hz
- Timing
- Beginning of systole
S2 ('dup')
- Duration
- 0.12 sec
- Frequency / pitch
- 50 Hz
- Timing
- End of clinical systole
S3
- Duration
- 0.1 sec
- Frequency / pitch
- Low-pitched
- Timing
- Early diastole, just after S2
S4 (atrial sound)
- Duration
- Not stated
- Frequency / pitch
- Low-pitched
- Timing
- Late diastole, just before S1