Auscultation - Heart Sounds

Blood flowing across the heart valves is laminar flow so that no sound is produced. The sounds heard on auscultation are the sound of the valve cusps snapping shut at the end of diastole (when the AV valves shut producing the 1st heart sound) and at the end of systole (when the Aortic Pulmonary valves shut producing the 2nd heart sound).

These sounds are conducted to the surface of the body and can be heard with the aid of a stethoscope. There are specific places on the anterior chest wall where the sound from each of the 4 valves can best be heard. These are not the surface markings of the valves but rather the points where the sounds are best conducted to. They are as follows:

• Aortic Valve – R 2nd ICS
• Pulmonary Valve – L 2nd ICS
• Tricuspid Valve – L sternal border
• Mitral Valve – 5th ICS MCL

These consist of two sharp sounds, S1 and S2, which differentiate systole from diastole and no other significant sounds will be heard.

A systole occurs when the ventricles fill with blood and the heart contracts. The sudden closure of the tricuspid valves and AV valves is caused by a decrease in pressure in the atria and a sharp increase in the intraventricular pressure which exceeds the pressure of the atria. This is the S1 sound. The ventricles continue to contract throughout systole forcing blood through the aortic and pulmonary semilunar valves.

S2 is formed at the end of systole when the ventricles begin to relax and the pressure in the aorta and pulmonary artery begin to exceed the intraventricular pressure. When this happens there is a slight back-flow of blood into the heart which causes the semilunar valves to snap shut, producing S2. These two sounds are to be considered single and instantaneous, indicating a normal healthy heart