Search the CAA website - somewhere you will find a list of approved (by them) cardiac specialists. You will have to have a private consultation with one of them, so its going to cost you. Your GP will do the referral to the consultant.
Whether or not you get your medical back will depend a lot on the exact nature of the heart condition that the attack has left you with. Surprisingly, if you are doing well it may not be a problem.
If you fly for recreation, which I assume to be the case, then be aware that the medical requirements for the NPPL are less stringent, so that may be an option for Plan B.
Good luck!