which tag is used to create animation (beating heart)?

Answer 1

Use CSS3 transitions and animations techniques

Answer 2

I suggest you use CSS to make the heart beat, and HTML to create the heart.
https://code.sololearn.com/Wp1bwtQcfVUO/?ref=app

Answer 3

https://code.sololearn.com/WickYe5wDp4W/?ref=app