One Heartbeat

The Story

Listening past the scratchy rub, the physician noted that Stina’s underlying heart sounds were normal: a clean ‘lub-dup,’ steady and unhurried. The rub was an extra noise laid over a well-timed cycle, not a sign the valves themselves were failing. Knowing the pump was mechanically sound let the team focus on the inflamed sac rather than chasing a valve problem that wasn’t there.

One heartbeat is a tightly choreographed alternation of contraction (systole) and relaxation (diastole). During diastole the chambers relax and fill; the atria then give a final top-off squeeze. When the ventricles contract (systole), rising pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. slams the atrioventricular valves shut — that closure is the first heart sound, ‘lub’ (S1) — and once ventricular pressure exceeds the pressure in the great arteriesBlood vessels that carry oxygenated blood away from the heart (except pulmonary arteries, which carr, the semilunar valves open and blood is ejected. As the ventricles relax, arterial pressure pushes back and snaps the semilunar valves closed — the second heart sound, ‘dup’ (S2). Every sound is a valve closing, and every closure is driven by a pressure gradient reversing. The cycle is the functional reason the chambers, valves, and wiring of the previous pages exist — and in pericarditis, the friction rub is simply an extra, abnormal sound riding along on this otherwise normal rhythm.

From Stina’s chart: On exam, Stina’s heart sounds were normal beneath the rub — the familiar ‘lub-dup’ of valves closing in sequence, the audible bookends of a single cardiac cycle.