what can happen is something like this

>have heart attack, which is when an artery clog prevents oxygen and blood from getting to the heart

>heart tissue impacted by clogged artery dies

>ED did revive person and get the heart beating again, but the dead tissue is still there and goes through the dying / fibrotic process over several days

>during the process the tissue is in a fragile state, so the heart can rupture

this is how carrie fisher died, a few days after the heart attack, for example