9 months after Stemi heart attack, Ejection fraction at 35%, exercising using electric bike, configured with 3 switcheable settings, 100% turbo, 90% turbo & 80% turbo.
Pulse rate with medication prevents me going much above 105bpm.
Question: Why if I do more than 20miles on any setting does my resting heart beat (normally 56bpm) stay elevated at 75bpm for several hours?
Thanks for your reply makes sense but...When I use the indoor non electrical assisted bike to cover a shorter distance (14 miles)..with much more strenuous effort, heart rate returns to normal resting heart rate well within 15 minutes not 5 hours. Guess I had better try slowly increasing in 1 mile increments future indoor runs to see if same problem kicks in at higher mileage.
Just want to make sure I am not going to experience a problem or do further damage to my heart.
Never noticed this prior to heart attack and I am sure I would have noticed.
high resting heart rate 
Very low resting heart rate
Statin side effects after cardiac arrest and stemi heart attack 
Irregular heart beat indicator
