Percentage of Heart muscle working

I just had a PET test and the results were that I am Low normal for the heart muscle. The nurse said my report said my heart muscle was working at 52%. I had angina in the past, was catherized, and had a stent put in my left front descending artery. The nurse also said that there was no change since my last PET scan in 2007. If normal is from 52% to 70% according to the nurse, what does the low normal reading tell me, and what can I do. I do walk and bike for exercise but do not eat well. Also I am a type 2 diabetic. I assume the heart muscle has damage from the past so what exactly is wrong with me and what more can I do to make it better?

[Cleveland Clinic]

I don't think your muscle is damaged because you never had a heart attack in the past (angina means pain due to low blood flow, not a heart attack).  Anything greater than 50% is normal, in my opinion.  Other than taking your meds and leading a healthy lifestyle, there really isn't anything else that you can do.