[dmkirwan]

Good idea to make a throwaway account for this question.

If I were in that situation I'd send a get well soon card and flowers. I wouldn't call or visit. Usually the only thing you have in common is work, so you're left to speak about either work or their heart attack. The latter is not really your business and the former is something they shouldn't be worrying about right now, so keeping these gestures one-way is a nice way to say "we're thinking of you and hope you get well soon" without the risk of putting them in an uncomfortable situation.

Good luck, and I hope they make a full recovery.