Should I avoid confined spaces when dh now has serious heart functioning failure?

Having recently caught Covid from attending a very small group of 8, I would not go. Had you asked before that I would have said to go. Covid is very infectious. Two of us in the group caught it but we don’t know who we got it from, just that we both got it at the same time and both attended that group.

I wouldn't go.
He's far more valuable than acquaintances or a hobby.
Cherish him.
All the best to both of you.

It depends on how vulnerable your husband is. I wouldn't go. Covid and flu jabs don't prevent you getting them, just hopefully lessen the effects.
Why don't you ask for advice from his clinicians, rather than strangers?

I am immunocompromised and have just spent eleven days in bed with a virus, everyone else in the family got over it in two days.
The fact that I am fully up to date with all my vaccinations did not stop me being very unwell.