The normal heart sounds are commonly described as "lub" and "dub," corresponding to distinct events in the cardiac cycle:
"Lub" (First heart sound, S1)
- Causes: The "lub" sound is produced by the closure of the atrioventricular (AV) valves, which include the mitral valve (left side) and tricuspid valve (right side).
- Timing: This sound occurs at the beginning of ventricular systole, when the ventricles contract to pump blood out of the heart. During this phase, the ventricles are actually emptying as they push blood into the aorta (left ventricle) and pulmonary artery (right ventricle).
"Dub" (Second heart sound, S2)
- Causes: The "dub" sound is created by the closure of the semilunar valves, which include the aortic valve (left side) and pulmonary valve (right side).
- Timing: This sound occurs at the end of ventricular systole and the beginning of ventricular diastole. At this point, the ventricles are beginning to fill with blood from the atria as the AV valves open (after the closing of the semilunar valves).
Summary of the Cardiac Cycle Phases:
- Ventricles Emptying: During the "lub" phase, as the ventricles contract and eject blood, they are emptying.
- Ventures Filling: During the "dub" phase, as the ventricular pressure decreases and the AV valves open, the ventricles begin to fill with blood from the atria.
In summary, the lub sound corresponds to the emptying of the ventricles, and the dub sound corresponds to the beginning of ventricles filling.
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