Heartbeat: CSS Keyframe Animation

Heartbeat

A double beat, a small lub and a bigger dub, then a rest, looping like a pulse. Good for a like button, a live badge or a health stat. Each beat rises fast and eases back down.

Also known as: heartbeat animation css, heart beat pulse, lub dub animation.

Color Base size 16px Dark background

HTML

<div class="kfa-heartbeat"><svg class="kfa-heartbeat-icon" viewBox="0 0 24 24" aria-hidden="true"><path d="M12 20.4 3.6 12.4a5.1 5.1 0 0 1 8.4-6.1 5.1 5.1 0 0 1 8.4 6.1Z" fill="currentColor"/></svg></div>

CSS

.kfa-heartbeat {
  --c: var(--kfa-color, #3b82f6);
  font-size: var(--kfa-size, 16px);
  display: grid;
  place-items: center;
  width: 5.5em;
  height: 5.5em;
  border-radius: 1em;
  background: var(--c);
  color: #fff;
  font-family: system-ui, sans-serif;
  font-weight: 700;
  box-shadow: 0 0.6em 1.4em -0.6em color-mix(in srgb, var(--c) 70%, transparent);
  animation: kfa-heartbeat-beat 1.5s infinite;
}
.kfa-heartbeat-icon {
  width: 2.6em;
  height: 2.6em;
}
@keyframes kfa-heartbeat-beat {
  0% { transform: scale(1); animation-timing-function: cubic-bezier(0.2, 0, 0.4, 1); }
  10% { transform: scale(1.14); animation-timing-function: cubic-bezier(0.5, 0, 0.6, 1); }
  20% { transform: scale(1.02); animation-timing-function: cubic-bezier(0.2, 0, 0.4, 1); }
  30% { transform: scale(1.24); animation-timing-function: cubic-bezier(0.45, 0, 0.55, 1); }
  50%, 100% { transform: scale(1); }
}

@media (prefers-reduced-motion: reduce) {
  .kfa-heartbeat, .kfa-heartbeat *, .kfa-heartbeat::before, .kfa-heartbeat::after, .kfa-heartbeat *::before, .kfa-heartbeat *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

Customizing this snippet

Color: set --kfa-color on the element or a parent. Currently previewing #3b82f6.
Base size: set --kfa-size. Every other dimension is in em, so the whole thing scales together. Currently previewing 16px.
Speed: change the duration on the transition or animation shorthand. Staggered delays are relative, so they keep their rhythm.
Reduced motion: the rule at the end of the CSS turns the motion off for people who asked their OS for less of it. Keep it.

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