Obviously you should check with your cardiologist, and with another one if you don't like his answer, but most heart patients I know (except the ones who've kept on smoking and eating the diet that got them into trouble in the first place) are exercising and doing great. I haven't had serious heart problems, but I do have an abnormal rhythm they watch closely, and my cardiologist (a former marathon runner, now ultradistance cyclist) urges vigorous exercise for me and nearly all his other patients. "Vigorous" varies from case to case, of course, but he's told me several times that he wants everybody exercising every day: "Say you're going to get out every day, and you'll probably make it five times a week, which is about what you need."