What does the S1 heart sound signify?

The S1 heart sound signifies the closure of the mitral and tricuspid valves. This sound occurs at the beginning of ventricular systole, marking the point when blood is pumped from the ventricles into the aorta and pulmonary artery. The closure of these valves prevents the backflow of blood from the ventricles into the atria during contraction, ensuring efficient forward flow into the circulatory system.

The S1 sound is often described as a "lub" sound and typically occurs just prior to the rise in pressure within the ventricles, confirming that the heart is preparing to enter the ejection phase of the cardiac cycle. Understanding the timing and significance of the S1 sound is crucial in interpreting normal heart function and identifying potential abnormalities during auscultation.