Final answer:
The third heart sound (S3) is rarely heard in healthy adults but can be normal in young adults, some athletes, and pregnant women. In older individuals, it may indicate heart pathology such as congestive heart failure.
Step-by-step explanation:
In a normal, healthy heart, the heart sounds one typically hears with auscultation are the first heart sound (S₁) and the second heart sound (S₂), corresponding to the closing of the atrioventricular valves and the semilunar valves, respectively. A third heart sound (S3) is less common and is not usually heard in healthy adults. However, an audible S3 can sometimes be normal in certain populations, including young adults, athletes, and pregnant women. Its presence in these individuals does not typically indicate pathology and may be due to enhanced ventricular filling. Conversely, if an S3 is discerned in an older individual, it may suggest the presence of conditions such as congestive heart failure and should be evaluated further by medical professionals.