Let us begin the orderly auscultation of our patient by listening with the diaphragm at the upper right sternal edge, and for a timing device we'll use the cotton swab on the carotid, so that one can clearly tell when systole is occurring. Let's all listen together.
Normal heart sounds
The first and second heart sounds at the upper right sternal edge are normal. They are single and are normal in intensity.
The second sound, S2, is normally louder than the first sound, S1, in the aortic area because the stethoscope is closer to the aortic valve than it is to the mitral valve.
The relative intensities of heart sounds may be clues to pathology. For example, a loud aortic closure may be seen in some patients with hypertension.
Moving heart
This is a graphic example of the left heart in the normal patient. In the animation that follows, we can appreciate that the first heart sound on the left side is associated with closure and tensing of the mitral valve, and the second heart sound on the left side is associated with closure and tensing of the aortic valve.
Cardiac cycle
Always keep in mind the events of the cardiac cycle.
In these left heart pressure tracings, S1 indicates the beginning of systole and coincides with closure of the mitral valve. S2 indicates the end of systole and the beginning of diastole, and coincides with closure of the aortic valve.
Both sounds are due to vibrations of the valve apparatus and surrounding cardiac structures and blood that result from valve closure and the ensuing deceleration of blood flow.
Discussion
What we heard at the upper right sternal edge is that cadence... Lub dub, lub dub, lub dub... The first heart sound and the second sound. The first sound due to closure of the mitral valve, the second sound due to closure of the aortic valve.
Those are the sounds you hear so clearly at the upper right sternal edge as the AV valves close - the beginning of systole, and the semilunar valves close at the end of systole. Note the first sound is a bit softer and the second one a bit louder... Lub dub, lub dub, lub dub.
Remember, it's lub (systole) dub, lub (systole) dub. You actually get those sounds in the beginning and end of the contraction period, and you think of the ventricle contracting. Let's listen together.
Graphic example
This is a graphic example of the normal first and second heart sounds. Let us listen together.