body {
  height: 100vh;
  display: grid;
  place-items: center;
}
.heart {
  position: relative;
  width: 100px;
  height: 100px;
  background-color: red;
  transform: rotate(225deg);
  margin: 50px;
  animation: beat 1s infinite ease-in-out;
}

.heart::before,
.heart::after {
  content: "";
  position: absolute;
  width: 100px;
  height: 100px;
  background-color: red;
  border-radius: 50%;
}

.heart::before {
  top: 50px;
  left: 0;
}

.heart::after {
  top: 0;
  left: 50px;
}

@keyframes beat {
  0% {
    scale: 0.5;
  }
  50% {
    scale: 1.3;
  }
}