Welcome @rhiannonmb.
Let me introduce you to a few members who can share their experiences to help you help your husband and yourself.

Please meet @lyndamm @jackj @crhp194 @thankful who have all had open heart surgery. I'm sure they will share the fears and concerns they had and maybe give you some insight how to support your husband. @cynaburst, too, has had major heart surgery at a young age. She also more recently supported her husband through a heart attack, surgery and rehab, so she can share from 2 perspectives.

You might find this discussion between @callalily74 @jackj useful too: "husband's open heart surgery" http://mayocl.in/2eb9MQt

Rhiann, I think to help your husband, the first thing is to meet him where he is (fear) and not where you want him to be (doing the operation). I can understand your urgency, but he may need more time to process and he shows this by denial. I don't think this means it's not on his mind. His denial must be a hard thing for the two of you to get beyond. Does he talk about his fears or does he refuse to talk about it altogether?