Lub-dub: the cycle you can hear
Press a stethoscope to the chest and you hear a repeating “lub-dub.” That's the cardiac cycle made audible. The “lub” is the first heart sound (S1) — the mitral and tricuspid valves snapping shut as systole begins. The “dub” is the second heart sound (S2) — the aortic and pulmonary valves closing as diastole begins.
Extra sounds carry meaning. A third heart sound (S3), a soft early-diastolic thud, can be normal in the young but in older adults often signals a stretched, volume-loaded ventricle — a clue toward heart failure. A whooshing murmur between the sounds points instead to turbulent flow across a diseased valve. So the rhythm and the spaces between “lub” and “dub” are a free, bedside readout of the cycle.
Ejection fraction: the fraction emptied
The ejection fraction (EF) answers a simple question: of the blood in the full ventricle, what fraction gets pumped out each beat? It's the stroke volume divided by the end-diastolic volume, written as a percentage. A normal left-ventricular EF is roughly 55–70% — the heart ejects a bit more than half of what it holds and keeps the rest in reserve.
Ejection fraction (EF) = (Stroke volume ÷ End-diastolic volume) × 100% NORMAL HEART SV = 70 mL, EDV = 120 mL EF = (70 ÷ 120) × 100% = 58% → normal (55–70%) WEAKENED HEART (reduced contractility) SV = 45 mL, EDV = 150 mL (dilated, fills more but empties poorly) EF = (45 ÷ 150) × 100% = 30% → significantly reduced