The S1 heart sound is caused by the sudden closure of the AV valves, which creates a pressure wave that travels through the heart and produces the characteristic sound. The mitral valve, located between the left atrium and ventricle, and the tricuspid valve, located between the right atrium and ventricle, are responsible for the S1 sound.
The , often colloquially described as the "lub" in the "lub-dub" of a heartbeat, is the first sound heard during a cardiac cycle. It marks the definitive onset of ventricular systole —the phase where the heart's lower chambers contract to pump blood to the body and lungs. What Produces the S1 Heart Sound? s1 heart sound