NC-Cutie,
With respect to whether or not your man can wait, there's a lot of "sexual activties" the two of you can engage in that aren't particularly strenuous, and which may satisfy his and your needs. Of course, I'm sure you'll worry about whether or not the less-strenuous activities will lead to something more strenuous (I'm a worrier too, sometimes, and I've been where you are now)...
For a few years now, I've been living with the classic symptoms of a bad aortic valve: shortness of breath and/or chest pain during certain kinds of physical exertion. The level of exertion has gradually gotten lower and lower over the years, yet I've continued to have sex as often as I can, within the usual limits of married and family life. There have been only three times when I have over-exerted myself during sex; each time I was VERY uncomfortable, but I rested and recovered. My heart and body gave me clear and unambiguous warning signs that I was pushing myself too far; I've learned to identify the warning signs much earlier in the game so I don't get as close to overexertion. Your body will give you the same warning signs. You're probably already familiar with them since you're in the process of recovery.
It sounds like your man is a sensitive and caring person who understands your situation and your concerns. I'm sure the two of you can talk about it, and arrange, in advance, to put on the brakes if you start to feel physically uncomfortable. For that matter, I wouldn't be surprised if you and your man already have an unspoken agreement to stop if either one of you has any kind of physical discomfort during sex, whether related to your hearts or some other parts of your bodies.
Finally, I'll launch into my standar lecture on the proper use of medical professionals: Don't be afraid to talk to your doctors about your concerns and fears, whether you think they're rational or irrational, trivial or non-trivial, personal or impersonal. You're paying your doctors a small fortune for their services; make sure you get your money's worth. Your doctors can only help what they've been told about. In my experience, most doctors appreciate a full and candid explanation of what their patients are feeling, and they're never shocked by what they hear.