My dads having a heart operation the last time I spoke to him I called him an old mutt and told him to f**k up, Do I apologise?

definitely, you need to apologize, he doesnt need to hear that kind of talk from you when hes about to have an operation

You told him to f**k "up"? What does that even mean? And why can't you use punctuation as well as an average 11 year old?

Yes. Always apologize. Even if he wasn't having a heart operation, you need to do things while you still can. No one knows how much time they have left, that is why you must utilize it in the present.

yes

If you feel that you should then you should.