Which of the following heart sounds would indicate possible heart failure upon auscultation?

The presence of a third heart sound (S3) upon auscultation can indicate possible heart failure, particularly in cases of left ventricular dysfunction or volume overload. The S3 sound is often described as a "ventricular gallop" and typically occurs just after the second heart sound (S2) during the rapid filling phase of the ventricles. In patients with heart failure, the inability of the ventricular muscle to accommodate blood during this phase can lead to this characteristic sound. It is particularly common in younger individuals and athletes, as well as in conditions that lead to heart failure, such as dilated cardiomyopathy.

The S4 heart sound, on the other hand, is associated with hypertensive heart disease and increased left ventricular stiffness, and while it may indicate some level of cardiac dysfunction, it is not as specific for heart failure as the S3. An extrasyllabic beat does not pertain to typical heart sounds and would not directly indicate heart failure. A friction rub is commonly associated with pericarditis and is not specific to heart failure either. Therefore, among the choices, the S3 heart sound is the definitive indicator of possible heart failure.