Look, the exercise you can do; yes, you'll get tired muuuuuuuuuuuuuuuucho, and for a long time.
If you are recently operated of this, no; don't do exercise, or anything that requires you to, by, more or less, a year - year and a half.
What intensity? Therefore, I would recommend that you start with something low, so you "auto-measure", if you feel able to: increase the pace; but don't overdo it. We speak of your life that is at stake.