Draw Me a Heartbeat

One beat, three waves

Each heartbeat is three coordinated electrical events. Both the ECG trace above and the FitzHugh-Nagumo ODE that Glyph compiles reproduce the same pattern.

WAVE 1

first 80 ms

P wave — atria fill

The sinoatrial node fires. Both atria contract, pushing blood into the ventricles. On the trace: a small smooth bump above the baseline.

WAVE 2

80 – 200 ms

QRS — the pump

The ventricles contract. The biggest electrical event in your body — visible as the sharp spike on every monitor. About 70 mL of blood leaves the heart in one beat.

WAVE 3

200 – 400 ms

T wave — recovery

The ventricles relax and reset their voltage. By 1000 ms (one full second) the cycle begins again. Awake, asleep, walking, dreaming — every second, all life long.

How Glyph drew it

Claude writes the JSON; Glyph integrates the ODE with RK4 and renders the trace. Same spec → byte-identical SVG, every platform, every run.

The Glyph spec JSON

// heartbeat.json — FitzHugh-Nagumo relaxation oscillator
{
  "version": "glyph/0.1",
  "title": "Heartbeat",
  "data": {
    "trajectory": {
      "shape": "trajectory",
      // dV/dt = V − V³/3 − W + 0.5
      "dxdt": "x - x*x*x/3 - y + 0.5",
      // dW/dt = ε(V + a − bW), with ε=0.08, a=0.7, b=0.8
      "dydt": "0.08*(x + 0.7 - 0.8*y)",
      "initial": { "x": -1.2,
                   "y": -0.6 },
      "time": { "min": 0,
                "max": 200,
                "samples": 2000 }
    }
  },
  "layers": [{
    "mark": "line",
    "encoding": {
      "x": { "field": "t" },   // time across
      "y": { "field": "x" }    // membrane V up
    }
  }]
}

Two coupled ODEs solved with 4th-order Runge-Kutta. The slow recovery variable W is what gives the trace its sharp spike followed by a long recovery — a real heart, not a sine wave. View on GitHub.

Glyph compiler output SVG

Glyph-rendered FitzHugh-Nagumo heartbeat trace, byte-locked across CI

Byte-stable across Ubuntu / macOS / Windows × Node 20 / 22. The 200-second integration window shows ~12 full FHN cycles — the same number of cycles a resting heart completes in 12 seconds at 60 BPM.

Your turn — prompts to try

Tell Claude what living thing or rhythm you want to see. Name the model, name the audience.

▸ Physiology

"Show me the difference between a healthy heart and one with arrhythmia. Use FitzHugh-Nagumo for both; in the second, change the I parameter to a value that breaks the rhythm. Side by side, same x-axis."

▸ Neuroscience

"Draw me a neuron firing. Use the Hodgkin-Huxley or FitzHugh-Nagumo model. Animate one action potential, then a burst of three in quick succession."

▸ Engineering

"Show me a van der Pol oscillator at three different μ values — small (almost sine), medium, and large (sharp relaxation). Three traces, same axes."

▸ Music

"Draw me the heartbeat alongside a metronome ticking at the same tempo. Show how a healthy heart isn't a clock — small natural variations in the inter-beat interval are a sign of life."