What are "lub" and "dub"? sound during

"Lub" and "dub" refer to the sounds produced by the heart during the cardiac cycle, specifically during the phases of heartbeats. 1. **Lub**: This sound, also known as the first heart sound (S1), occurs when the atrioventricular (AV) valves (the mitral and tricuspid valves) close at the beginning of ventricular contraction (systole). It is a lower-pitched sound and is typically louder than the second sound. 2. **Dub**: This sound, known as the second heart sound (S2), occurs when the semilunar valves (the aortic and pulmonary valves) close at the end of ventricular contraction and the beginning of ventricular relaxation (diastole). The "dub" sound is shorter and higher-pitched compared to the "lub." These sounds can be heard using a stethoscope and are important indicators of heart function. Abnormalities in these sounds can indicate various heart conditions.