What is the first heart sound known as?

The first heart sound is referred to as "Lub." This sound occurs when the atrioventricular (AV) valves, specifically the mitral and tricuspid valves, close at the beginning of ventricular contraction or systole. The "Lub" sound is typically lower in pitch and longer in duration compared to the second heart sound, known as "Dub," which is associated with the closure of the semilunar valves at the end of systole. Understanding the heart sounds is crucial in assessing cardiac health, as they provide important information about valve function and the overall state of circulation.