The left ventricle is driven by a real time-varying elastance model — the same mechanism used to derive the classic cardiology pressure-volume loop, but shown here as it unfolds moment-to-moment (a Wiggers-diagram view) alongside the actual blood flow it produces through the circulation:
P_LV(t) = E(t)·(V_LV − V0)
E(t) = (Emax−Emin)·En(tn) + Emin [double-Hill normalized elastance]
Q_mv = max(0, Pven−P_LV)/Rmv dV_LV/dt = Q_mv − Q_av
Q_av = max(0, P_LV−Pao)/Rav
dPao/dt = (Q_av − Pao/Rsys)/Cart [2-element Windkessel]
The mitral valve opens only while venous pressure exceeds ventricular pressure (diastolic filling); the aortic valve opens only once ventricular pressure exceeds aortic pressure (systolic ejection). Between those windows volume is fixed — the isovolumic phases of the real cardiac cycle emerge from the valve inequalities themselves, not from a scripted shape. Ejected flow charges a lumped arterial "Windkessel" — a compliant vessel draining through peripheral resistance — which is what produces the arterial pressure's characteristic fast systolic upstroke, dicrotic notch at valve closure, and slow diastolic runoff, and is also what sets the actual speed of the flow particles you see moving through the vessels.
- Heart rate — cycles per minute; a shorter cycle leaves less time for diastolic filling, which can itself cap end-diastolic volume and stroke volume.
- Contractility (Emax) — steepness of the end-systolic elastance; higher values eject further against the same afterload, raising stroke volume and cardiac output.
- Preload — venous filling pressure; more stretch before contraction raises end-diastolic volume (Frank–Starling), widening stroke volume without changing the muscle itself.
- Afterload (systemic resistance) — the load the ventricle ejects against; raising it slows ejection and raises mean arterial pressure while shrinking stroke volume.
- Arterial compliance — vessel stiffness; a stiffer (lower-compliance) artery produces a higher pulse pressure for the same stroke volume, exactly as aging arteries do physiologically.