Mine was done 19 years ago - staples, wires, and whatever they used to close up the sternotomy. It's hard to see unless you intentionally look for it.
I took my daughter to a father-daughter dinner a month post-op, and other fathers noticed the rather red scar. This was a real conversation starter, because a handful of other fathers opened their shirts to show me theirs.
From reading about the new methods of closing, it doesn't sound like the scar is much of a deal at all. Unless your husband is a model, I don't think he should worry (plus, as others have said, growing hairs back over the incision help, and, I guess, so would a touch of makeup if he really wants to hide it). I haven't tried tanning my chest for some years, so I don't know if the scar shows as a white strip against a tanned chest.