beatingHeart.css

/* Heart beating - set to beat infinite times */
/* Two shapes create the heart - .back and .heart */

<style>

  .back {
    position: fixed;
    padding: 0;
    margin: 0;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: white;
    animation-name: backdiv;
    animation-duration: 1s;
    animation-iteration-count: infinite; 
    
  }

  .heart {
    position: absolute;
    margin: auto;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    background-color: pink;
    height: 50px;
    width: 50px;
    transform: rotate(-45deg);
    animation-name: beat;
    animation-duration: 1s;
    animation-iteration-count: infinite;
    
  }
  
  .heart:after {
    background-color: pink;
    content: "";
    border-radius: 50%;
    position: absolute;
    width: 50px;
    height: 50px;
    top: 0px;
    left: 25px;
    
  }
  
  .heart:before {
    background-color: pink;
    content: "";
    border-radius: 50%;
    position: absolute;
    width: 50px;
    height: 50px;
    top: -25px;
    left: 0px;
    
  }

  @keyframes backdiv {
    50% {
      background: #ffe6f2;
      
    }
  }

  @keyframes beat {
    0% {
      transform: scale(1) rotate(-45deg);
      
    }
    50% {
      transform: scale(0.6) rotate(-45deg);
      
    }
  }

</style>

<div class="back"></div>
<div class="heart"></div>