Which sound is primarily associated with heart failure during diastole?

The third heart sound (S3) is primarily associated with heart failure during diastole. This sound occurs shortly after S2 and is produced when blood rapidly fills the ventricles, particularly in cases where there is increased volume overload or decreased ventricular compliance, which is common in heart failure.

In heart failure, the ventricles may be less effective at managing the volume of blood returning to the heart. As a result, the S3 sound becomes more pronounced. It is often described as a "gallop" rhythm and can indicate that the heart is struggling to fill properly, a hallmark of diastolic dysfunction.

The other heart sounds, S1 and S2, are normal components of heart function and are not specifically indicative of heart failure. S4, which occurs just before S1, is associated with decreased ventricular compliance and is more frequently heard in patients with left ventricular hypertrophy or other conditions leading to stiffness of the ventricles, rather than directly signaling heart failure during diastole. Therefore, S3 serves as a significant clinical indicator in the assessment of heart failure.