Lub-dub Sound Instant

| Feature | S1 ("Lub") | S2 ("Dub") | | :--- | :--- | :--- | | | Closure of Mitral & Tricuspid valves | Closure of Aortic & Pulmonic valves | | Phase | Marks onset of Systole | Marks onset of Diastole | | Sound Quality | Lower pitch, longer duration | Higher pitch, shorter, sharper | | Best Heard At | Cardiac Apex (5th ICS, MCL) | Cardiac Base (2nd ICS, RSB) |

The first sound, , is a lower-pitched, slightly longer sound that marks the beginning of systole (the heart's contraction phase). lub-dub sound

Understanding these sounds is the foundation of cardiac auscultation. | Feature | S1 ("Lub") | S2 ("Dub")