<div class="heart-box">
  <div class="heart"></div>
</div>
$size: 100px;

html, body {
  height: 100%;
}

.heart-box {
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
}

.heart {
  animation: .7s ease-in 0s infinite alternate throb;
  width: $size;
  height: $size;
  background: #f00;
  transform: rotateZ(45deg);
  position: relative;
  
  filter: drop-shadow(2px 2px 2px #000);
    
  &::before, &::after {
    content:'';
    width: $size;
    height: $size;
    background: #f00;
    position: absolute;
    border-radius: 50%;
  }
  
  &::before {
    top: 0;
    left: -50%;
  }
  &::after {
    top: -50%;
    right: 0;
  }
}

@keyframes throb {
  from {
    transform: rotateZ(45deg) scale(1, 1);
  }
  to {
    transform: rotateZ(45deg) scale(1.3, 1.3);
  }
}
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