To facilitate the correct identification of systole and diastole, as you auscultate the chest, palpate the right carotid artery in the lower third of the neck with your left index and middle fingers—S1 falls just before the carotid upstroke and S2 follows the carotid upstroke. Be sure to compare the intensities of S1 and S2 as you move your stethoscope through the listening areas above.

■ At the base, you will note that S2 is louder than S1 and may split with respiration. At the apex, S1 is usually louder than S2 unless the PR interval is prolonged.

■ By carefully noting the intensities of S1 and S2, you will confirm each of these sounds and thereby correctly identify systole, the interval between S1 and S2, and diastole, the interval between S2 and S1.

The correct timing of systole and diastole is the fundamental prerequisite to identifying events in the cardiac cycle. Review the guides to auscultation on next page and learn the tips for identifying heart murmurs which follow in the next section.

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