28. The heart sounds. Phonocardiography (PCG)
The heart makes sounds when it beats. More specifically, what we consider “heart sounds” are actually the sound of turbulent blood flow which occurs as the valves close. These sounds are very silent but can be heard with a stethoscope, which amplifies the sounds. This is called auscultation and is an important part of physical examination of the patient.
The heart makes two sounds in healthy people. These are called the first and second heart sounds, or S1 and S2. An additional two sounds can be heard in pathological cases. These are the third and fourth heart sounds, S3 and S4.
The different heart sounds occur at specific times in the cardiac cycle. All four sounds can be heard anywhere at the area of the heart on the chest.
First heart sound:
The first heart sound is physiological. The sound comes from the vibration which occurs when the atrioventricular valves close. It occurs right after the R wave on the ECG, right at the beginning of the systole.
Second heart sound:
The second heart sound is physiological. The sound comes from the vibration which occurs when the semilunar valves close. It occurs right after the T wave on the ECG.
The aortic and pulmonary valves don’t close at exactly the same time and so the second heart sound has two components, an aortic component and a pulmonary component.
Third heart sound:
The third heart sound can be physiological or pathological. It can be physiological in young individuals and pregnant women. The sound comes from the rapid ventricular filling.
Fourth heart sound:
The fourth heart sound is always pathological. The sound comes from the atrial systole.
Events of the cardiac cycle:
| Phase | Phase name | Part of the cardiac cycle | Semilunar valves | Atrioventricular valves | Corresponding EKG wave | Corresponding heart sound |
| 1 | Isovolumetric contraction | Systole | Closed | Closed | QRS | S1 |
| 2 | Fast ejection | Systole | Open | Closed | – | – |
| 3 | Slow ejection | Systole | Open | Closed | T | – |
| 4 | Isovolumetric ventricular relaxation | Diastole | Closed | Closed | – | S2 |
| 5 | Rapid ventricular filling | Diastole | Closed | Open | – | S3 (pathological) |
| 6 | Slow ventricular filling | Diastole | Closed | Open | – | – |
| 7 | Atrial systole | Diastole | Closed | Open | P | S4 (pathological) |
Heart murmurs
Heart murmurs are sounds produced by turbulent blood flow through pathological (abnormal) valves. They usually sound like whooshing or swishing and can be heard between the heart sounds. There are two pathologies that can occur with heart valves:
- They can be stenotic – meaning that their lumen is very narrow
- They can be insufficient or regurgitate – meaning that they can’t close properly, causing blood to flow backward in the heart
As an example; if an aortic valve is stenotic a whoosh sound can be heard when blood is ejected through it in systole.
Murmurs can be systolic or diastolic, depending on when in the cardiac cycle it’s heard.
Punctum maxima:
Each heart valve has a specific point on the chest where the murmurs it makes is best heard. These points are called the punctum maxima.
| Valve | Punctum maximum |
| Mitral valve | 5th intercostal space, midclavicular line, left side |
| Tricuspid valve | 4th intercostal space, parasternal line, left side |
| Pulmonary valve | 2nd intercostal space, parasternal line, left side |
| Aortic valve | 2nd intercostal space, parasternal line, right side |
Phonocardiography
Phonocardiography refers to the use of sensitive microphones to record heart sounds and murmurs that are too silent or too low in frequency to be heard with the human ear and display them as waves on a paper. Some sounds the heart makes is in the infrasound spectrum, meaning that it’s too low frequency to be heard by the human ear. This technique is obsolete and is not used anymore.