Final answer:
The first normal heart sound heard during auscultation is Sā, which is the sound of the atrioventricular valves closing during ventricular systole.
Step-by-step explanation:
When assessing heart sounds, the first normal heart sound is Sā. This sound, commonly referred to as the lub," corresponds to the closing of the atrioventricular valves during the ventricular systole phase of the heart cycle. It is followed by the second heart sound, S2, known as the dub, which occurs when the semilunar valves close during ventricular diastole. The subsequent sounds, S3 and S4, are not typically heard in healthy individuals.
S3 can be associated with the flow of blood into the atria or ventricles, or the tension of the chordae tendineae, and may indicate conditions such as congestive heart failure if present later in life. The sound S4 is associated with the atria contracting and pushing blood into a stiff or hypertrophic ventricle, signaling potential left ventricular failure.