How safe are cortisone shots after a heart attack?

Yes, but depends. Local cortisone injections for joint inflammation/pain can be safely given to most heart atttack patients after a few weeks in most cases. Often the cortison is mixed with a local anesthetic to immediately relieve the pain and care must be taken to not use an anesthetic with epinephrine, which can stimulate the heart.The usual care must be taken to prevent bloodstream injection when given.
That depends. Cortisone injections are usually safe - and if you are dependent on them it is important to maintain a consistent dosing regimen. You should talk to your doctor to be certain you are ready - or that you even need them at all.