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Heartbeat Pulse Animation (Biologically Accurate Scale Expression)

About This Expression

This expression simulates a realistic human heartbeat by recreating the natural β€œlub-dub” rhythm of cardiac motion. Unlike a basic sine wave that pulses evenly, this setup produces two distinct beats per cycleβ€”closely matching how the heart actually contracts and relaxes.

The motion is driven by exponentially decaying sine waves, which creates a sharp initial contraction (systole) followed by a softer secondary pulse (diastole). The result feels organic, medical, and convincing rather than mechanical.

Because the animation is applied to Scale, it works perfectly for icons, shapes, UI elements, and anatomical visuals.

Expression

bpm = 72; // Beats Per Minute
intensity = 15; // How much to scale up (in %)
period = 60 / bpm;
t = time % period;
// Simulation constants
decay = 20; // How snappy the beat is
gap = 0.35; // Time delay between lub and dub in seconds
pulse1 = Math.sin(t * 20) * Math.exp(-decay * t);
if (pulse1 < 0) pulse1 = 0;
t2 = t - gap;
pulse2 = 0;
if (t2 > 0) {
 pulse2 = Math.sin(t2 * 20) * Math.exp(-decay * t2);
 if (pulse2 < 0) pulse2 = 0;
}
totalPulse = pulse1 + (pulse2 * 0.8);
s = value[0] + (totalPulse * intensity);
[s, s];

How We Use This Expression

Step 1: Select the Layer to Animate

This expression can be used on:

  • Shape layers
  • Text layers
  • Icons or logos
  • Heart graphics or UI elements

Select the layer you want to pulse.

Step 2: Apply the Expression to Scale

  1. Press S to reveal Scale
  2. Hold Alt (Windows) / Option (Mac) and click the Scale stopwatch
  3. Paste the heartbeat expression
  4. Click outside the editor to apply

The layer will immediately start pulsing in a realistic heartbeat rhythm.

Step 3: Set the Heart Rate

Inside the expression, adjust:

bpm = 72;

Common values:

  • 60–70 β†’ resting heartbeat
  • 80–100 β†’ excitement or stress
  • 110+ β†’ intense or emergency state

The animation updates instantly.

Step 4: Control Pulse Strength

Adjust:

intensity = 15;
  • Lower values β†’ subtle UI pulses
  • Higher values β†’ dramatic, visible beats

Great for both medical visuals and stylized animations.

Step 5: Refine the Feel

You can fine-tune realism by adjusting:

  • decay β†’ sharper or softer beats
  • gap β†’ spacing between lub and dub

This lets you match medical accuracy or artistic style.

Step 6: Combine With Other Effects

For stronger impact, pair this with:

  • Glow or Fill color changes
  • Opacity flicker on each beat
  • EKG line animations
  • Sound effects synced to BPM

The expression keeps perfect timing.

Best Use Cases in After Effects

  • Medical and health animations
  • Heart rate monitors & EKG visuals
  • Fitness or wellness apps
  • Emotional UI feedback
  • Logo pulses and intro stings

Why This Approach Works So Well

This expression works because it models real physiological behavior, not just looping math. The eye recognizes the double-beat instantly, making the motion feel alive and believable.

You get:

  • Accurate rhythm
  • Smooth looping
  • Full art-direction control
  • Zero plugins or keyframes

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