Which of the following heart sounds may indicate heart failure?

The S3 gallop is a heart sound that can indicate heart failure, particularly in cases of volume overload or decreased left ventricular function. This third heart sound occurs when blood fills the ventricles during the rapid filling phase, and its presence often suggests that the ventricles are not functioning effectively to handle the blood volume. In the context of heart failure, the S3 sound can reflect elevated pressures in the left atrium and increased fluid volume in the heart, thus serving as a clinical marker for heart failure.

The presence of a normal S1 and S2 does not suggest heart failure; instead, it indicates the absence of abnormal heart sounds, which can mislead clinicians into thinking the heart is healthy. An opening snap may be associated with mitral stenosis rather than heart failure specifically, as it is a characteristic sound that signifies the abrupt halt of valve opening. Frequent extrasystoles, or premature contractions, while they can occur in various cardiac conditions, are not a definitive sign of heart failure themselves. Thus, the S3 gallop stands out as a key indicator associated with the hemodynamic changes seen in heart failure.