animate.css/source/attention_seekers/heartBeat.css

@keyframes heartBeat {
  0% {
    transform: scale(1);
  }

  14% {
    transform: scale(1.3);
  }

  28% {
    transform: scale(1);
  }

  42% {
    transform: scale(1.3);
  }

  70% {
    transform: scale(1);
  }
}

.heartBeat {
  animation-name: heartBeat;
  animation-duration: 1.3s;
  animation-timing-function: ease-in-out;
}