De or het cardioversie?

The correct Dutch article is:

de cardioversie

Rule Words ending in -tie and -sie: almost always de. See the rule

How to use cardioversie

the cardioversiede cardioversie
this cardioversiedeze cardioversie
that cardioversiedie cardioversie
our cardioversieonze cardioversie
your cardioversiejouw cardioversie
every cardioversieelke cardioversie
which cardioversie?welke cardioversie?
a big cardioversie / the big cardioversieeen grote cardioversie, de grote cardioversie