I am in the same situation. Heart surgery 20 years ago and have been flying on a Group 1 GP declaration since. Now depending on which of 3 different CAA pieces of paper I choose to believe, I can a) fly my aeroplane, or b) not fly my aeroplane until I have an LAPL medical involving spending £500+ on an exercise ECG and a cardiologists report.
There is different wording between the Declaration form, the Guidance notes on the CAA website and the ANO Section 163.
It's a mess