- With each heart-beat, the detectable heart sounds are produced.
- These sounds represent the auscultatory events of the cardiac cycle.
- Heart sounds can be amplified and recorded by placing an electronically amplified microphone on the chest.
- The recording of such sounds is called a phonocardiogram.
- There are four heart sounds associated with the cardiac cycle.
- Among them only the first and second heart sounds (traditionally referred to as lubb and dupp, respectively) can be heard easily with a stethoscope.
First heart sound
- It is more complex, lower in pitch and lasts longer than the second sound.
- It occurs as a result of the ventricles contracting which forces blood against auriculo-ventricular valves.
- This causes them to bulge backward towards the atria until the chordae tendinae abruptly stop the bulging.
- The elastic nature of the valves then causes the blood to bounce forward into each ventricle.
- This causes the blood, ventricular walls and valves to vibrate.
- It is these vibrations that produce the first heart sound.
Second heart sound
- It is high in pitch.
- It results from the sudden closing of the semilunar valves.
- This allows them to bulge backward towards the ventricles until their elastic stretch recoils the blood back into the arteries.
- This recoil produces vibrations that reverberate back and froth between the heart walls, arteries and valves.
- When the vibrations contact the chest wall, they create what can be heard as the second heart sound.
- The second heart sound is heard best over the second inter-costals space, where the aorta is closest to the surface.
- Immediately after the second sound there is a short interval of silence.
Third heart sound
- It is a low-pitched sound which is heard occasionally.
- It is caused by the vibration of the ventricular walls after the atrio-ventricular valves open and the blood pushes into the ventricle.
- This sound is heard best in the tricuspid area.
Fourth heart sound
- It is usually not heard with an unamplified stethoscope in normal heart.
- It is caused by the blood rushing into the ventricles.
- Heart sounds are important tools in diagnosing valvular abnormalities.
- Any unusual sound is called murmur.