How to use: Pick a preset, then push the sliders and watch all three
traces change together — nothing here is a decoration, they all come out of the same
beating model.
The three traces. The green trace is an
ECG: the flat line before each spike is the P wave (the atria contracting), the tall
spike is the QRS complex (the ventricles contracting) and the slow hump after it is
the T wave. The pink trace is artery pressure,
the cuff reading in millimetres of mercury — watch the little dip called the
dicrotic notch, which is the moment the aortic valve slams shut.
The blue loop is the left ventricle's pressure against its
volume; the area inside it is the work the heart does.
Watch the valves. During isovolumetric contraction and
isovolumetric relaxation every valve is shut, so the heart is squeezing hard but no
blood is moving at all. Turn on slow motion to see it.
Press Space to pause or resume, and S for slow motion.Notice: cardiac output = heart rate × stroke volume, and the two cannot rise together forever. At rest the heart moves about 67 mL a beat at 70 bpm — around 4.7 L/min. Raise the rate to 140 and output reaches roughly 6.9 L/min, but stroke volume has already slipped to about 49 mL: every beat has less time to fill. Push on to 200 and the rate has nearly trebled while output has only gone from 4.7 to 8.4 L/min, because each beat is now moving 42 mL instead of 67 and the ejection fraction has fallen from 55% to 35%. Meanwhile the arterial trace climbs past 190/179 — this model has no baroreflex, so nothing pulls the pressure back down when the rate rises. Give it a few seconds to settle: pressure and volume need a moment to re-equilibrate, just as in a real circulation. And when the atria stop helping, as in atrial fibrillation, the ventricles can fill only by passive suction: at the same heart rate each beat moves about a fifth less, and output falls with it.