heart beat heartbeat and heart beating

Question

Is there any difference (or wrong) among the following:

1. It's heart beat has stopped.
2. It's heartbeat has stopped.
3. It's heart beating has stopped.
4. It's heart has stopped beating.

Answer 1

You need its, not it's! (Its is the possessive pronoun. It's means "it is".)

2. Its heartbeat has stopped.

is both perfect and colloquial.

4. Its heart has stopped beating.

is perfect English, but perhaps a little less colloquial.

The other two are wrong.