Two piston pumps share one bench and one beat. The right pump pushes dark blood through the lungs; the left pump pushes bright blood through the body. Four valves keep every drop moving one way.
Every beat runs through the same five phases, and the valves decide which one you are in. A valve opens only when the pressure behind it is higher than the pressure in front. The phase the bench is in now is shaded.
The vital signs of the last full beat, then every compartment of the circulation: its pressure now, its range over the beat, and the blood it holds.
| Compartment | Blood | Pressure now | Range, last beat | Volume now | Volume, last beat |
|---|
Physiologists draw the same beat two ways. On the left is pressure against time, the chart Carl Wiggers published in 1915. On the right is pressure against volume: each beat traces a loop, and the area inside is the work the ventricle does. Both are redrawn from the bench after every beat.
The arithmetic. Each chamber is a time-varying elastance, P = E(t)(V − V₀). Arteries and veins are compliances; vessels and valves are resistances, and valves only pass blood forwards. The bench integrates these equations every half millisecond while you watch.
The parameters, tuned to a resting adult: about 115/80 mmHg, 70 mL per beat and 5 L a minute at 72 beats. The stenosis and leak are stronger than most patients have, so the change is easy to see.
Heart muscle, the coronary arteries and the electrical system. The lungs only recolour the blood; breathing is not modelled. The contraction curve is simple, so isovolumic contraction runs about twice as long as in a real heart.