I contracted viral myocarditis a while ago and was out of training for 12+ months. I was referred to the Cardiac Athletes website by forumites and found it helpful. I also found British Heart Foundation (I spoke to their head nurse, Siobhan I think that her name was) who more helpful than my GP. He was convinced that I "just had asthma".
I do HR training which helped in my eventual diagnosis as I was able to take in my training log and show them the changes in my HR etc. Long term, it might be worth thinking about HR training (apart from just keeping track of your HR) as the focus is on mileage at low intensity HR.
Before I became ill, I'd been doing 40 - 50 m per week and was in my last few weeks of taper before a mara. When I started back, I could barely walk to the end of the road - I'd lost all my stamina and fitness after being out of action for so long. You have to forget what you used to be able to do and just focus on what you can do at the moment / this week. Start slowly - don't worry that it's more walk than run, just do what feels comfortable - better to do a few sessions a week at a slower pace than one that pushes you too much. You'll soon build up fitness etc, it just takes patience.
Good luck