The simple idea
- S3 — a "flood" sound. Blood pours very quickly into a ventricle that is already full or floppy. Normal in children, young adults and pregnancy; in older people it often means heart failure. Rhythm: "lub‑dub‑ta" ("Ken‑tuc‑ky").
- S4 — a "push against a wall" sound. The atrium gives a hard final push into a stiff ventricle, just before "lub." Common with long‑standing high blood pressure. Rhythm: "ta‑lub‑dub" ("Ten‑nes‑see"). There is no S4 in atrial fibrillation, because the atrium no longer pushes.
- Opening snap — a narrowed mitral valve snapping open, just after "dub" (mitral stenosis).
- Clicks — a sharp click when an abnormal valve opens (e.g. a bicuspid aortic valve), or when a floppy mitral valve pops back (mitral valve prolapse).