Which heart sound occurs in late diastole just before S1?

The heart sound that occurs in late diastole just before S1 is S4, also known as the "atrial gallop." This sound is produced by the vigorous contraction of the atria, which pushes blood into a still or stiff ventricle. It typically occurs just before the first heart sound (S1), which marks the beginning of systole and the closure of the mitral and tricuspid valves.

S4 is often associated with conditions that cause decreased ventricular compliance, such as hypertension or left ventricular hypertrophy, making it more common in older adults or individuals with certain cardiac conditions. Recognizing the presence of S4 can be important in assessing the cardiac health of a patient, as it may indicate underlying issues that warrant further investigation.

In contrast, S1 marks the closure of the atrioventricular valves at the start of ventricular contraction, S2 marks the closure of the semilunar valves at the end of ventricular systole, and S3, often termed a "ventricular gallop," occurs early in diastole and is associated with rapid filling of the ventricles. Understanding the timing and characteristics of these heart sounds is crucial for effective cardiovascular assessment.