Which chambers contract during the heart beat LUB?

The heart contracts and pumps blood in a synchronized rhythm of systole and diastole. During one heartbeat, the "LUB" sound heard corresponds to the first heart sound (S1). This occurs during systole, when the atria have already contracted and filled the ventricles with blood, and then the ventricles contract and increase their pressure. As a result, the mitral valve and the tricuspid valve close with force, creating the "LUB" sound. So, during the "LUB" sound of a heartbeat, it is primarily the ventricles that contract, leading to the closure of the atrioventricular valves (the mitral and tricuspid valves) and the generation of the first heart sound.