i am 55 years old been running for 7 years ran one full marathon average 25 to 30 miles per week, On Oct 1st 2015 i was in the gym running on treadmil at 6.5 mph and had a heart attack, thankfully a trainer and nurse did CPR and defibilator and brought me back my main left attery was 95% blocked. i had one stent sent home 2 days later back to work in 4 days. yesterday got all clear from the doctor no heart damage, blood pressure 110/70. i ran very slow 2 mile yesterday. my question is when should i step it up. the fear is worse than the heart attack