Heart Simulator: Cardiac Cycle, Wiggers Diagram, PV Loop and ECG Rhythms

A free heart and circulation simulator for students and health professionals: an animated heart synced to a Wiggers diagram, pressure-volume loops with preload, afterload and contractility sliders and disease presets, an ECG rhythm trainer with calipers, QTc and a quiz, and a hemodynamics calculator.

For learning only. A teaching model of the heart and circulation: not a medical device, not for diagnosing anyone or making clinical decisions.

One heartbeat, slowed down. The heart on the left and the Wiggers diagram on the right are the same moment: watch the valves open and close exactly where the pressure lines cross. Click or drag on the diagram to move through the beat.

Heart rate: per minute
Speed: Slow motion makes the short phases (the valves) easy to follow.
Moment in the beat: Moving it pauses the animation.

How the heart simulator works

The Cardiac cycle and Pressure-volume loop tabs run the same model: a lumped (“0-D”) circulation of the kind used in physiology teaching and research. The left ventricle and left atrium are time-varying elastances (Suga and Sagawa): their stiffness rises as the muscle contracts and falls as it relaxes, so the pressure in them follows from their volume. The arteries are a three-element Windkessel (a characteristic impedance, a compliance and the systemic vascular resistance). The veins, lungs and right heart are lumped into one large compliant pool that refills the left atrium. The valves are one-way, with pressure drops from the simplified Bernoulli equation, so a narrow valve gives a realistic gradient and a leaking valve lets blood back through its hole.

ventricle \(\displaystyle P_{LV}(t)=e(t)\,E_{es}\,(V-V_0)+\big(1-e(t)\big)\,A\big(e^{B(V-V_0)}-1\big)\)
valve \(\displaystyle \Delta P = 4v^2,\quad v=\frac{Q}{A_{valve}}\)
arteries \(\displaystyle C\,\frac{dP}{dt}=Q_{ao}-\frac{P-P_{v}}{R_{SVR}}\)
loop \(\displaystyle SV = EDV-ESV,\quad EF=\frac{SV}{EDV},\quad E_a=\frac{P_{es}}{SV},\quad SW=\oint P\,dV\)
QTc \(\displaystyle QT_{c,B}=\frac{QT}{\sqrt{RR}},\quad QT_{c,F}=\frac{QT}{\sqrt[3]{RR}}\)
hemodynamics \(\displaystyle SVR=\frac{80\,(MAP-CVP)}{CO},\quad DO_2=CO\times(1.34\,Hb\,S_aO_2+0.003\,P_aO_2)\times10\)

What to look at

  • The valves follow the pressures. The mitral valve shuts when ventricular pressure rises above atrial pressure (S1), the aortic valve opens when it rises above aortic pressure, and it shuts again (S2, with the small dicrotic notch) when the ventricle relaxes. Between them the volume does not change: the isovolumic phases.
  • Frank-Starling. Raise the preload and the loop gets wider: a fuller ventricle ejects more. Press Caval occlusion to squeeze off the returning blood: the loops shrink and their top-left corners slide down one straight line, the ESPVR. That is how its slope (Ees, contractility) is measured in the lab.
  • Afterload and coupling. Raising SVR makes the Ea line steeper: higher pressure, smaller stroke volume. Ees/Ea near 1-2 is the efficient range.
  • Diseases change the shape. Stenosis makes the loop tall (aortic) or small and high-pressured in the atrium (mitral); regurgitation removes the straight isovolumic sides; a stiff ventricle rides up a steep EDPVR.

ECG rhythms

The strip is drawn wave by wave (P, Q, R, S, T as smooth bumps, in the style of McSharry and colleagues' synthetic ECG) by a beat-by-beat generator that follows each rhythm's rule: the PR lengthening of Wenckebach, the sudden drop of Mobitz II, the independent atria and ventricles of complete block, the compensatory pause after a PVC. Rates: 300 ÷ big squares or 1500 ÷ small squares between two R waves. Normal values: PR 120-200 ms, QRS under 120 ms, QTc under 450 ms (men) or 460 ms (women), over 500 ms high risk (AHA/ACCF/HRS 2009). Only lead II is shown; real diagnosis needs all twelve leads and the patient.

Sources and limits

Elastance curve: Stergiopulos, Meister and Westerhof (1996), with its time to peak scaled so electromechanical systole follows Weissler's QS2 = 546 − 2.1 × HR ms. Pressure-volume concepts: Suga and Sagawa (1974); Klabunde, Cardiovascular Physiology Concepts; Guyton and Hall. Severity thresholds: 2020 ACC/AHA valvular heart disease guideline (severe aortic stenosis: area < 1 cm², mean gradient ≥ 40 mmHg; severe mitral regurgitation: EROA ≥ 0.4 cm², regurgitant volume ≥ 60 ml, fraction ≥ 50%; severe aortic regurgitation: EROA ≥ 0.3 cm²; severe mitral stenosis: area ≤ 1.5 cm²). BSA: Mosteller (1987) and Du Bois. The model has no right ventricle of its own, no reflexes (baroreceptors) unless a preset sets them by hand, no coronary flow, and no blood viscosity or inertia except at the aortic valve; numbers are typical, not anyone's. The right side of the drawn heart follows the left side's timing.

Everything runs on your device and nothing is uploaded. Heart Rate Zones · Body Surface Area · Fluid Simulator · More MES tools

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