There was a question that was asked in the expert forum about heart rate recovery after exercise:
http://www.medhelp.org/posts/Heart-Disease/Exercise/show/1461687
The dr gave this link as a reference http://www.livestrong.com/article/253521-heart-rate-drop-in-first-minute-after-exercise/ This might be helpful for you regarding heart rate recovery.
If you dropped 12 beats or fewer in the first minute post-exercise, that would be considered abnormal heart rate recovery.
I would make a chart or spreadsheet and use a reliable monitor and check your hr at the beginning, then middle of your workout and get to 85% of your maximal predicted heart rate; take your stats, then in your cooldown take your stats and 1 minute after exercise is done.
If it continues not to go down at least 12 beats, a visit to a cardiologist for a full cardiac workup may be in order just as a precaution.
Btw, have you had your blood done lately to see how your cholesterol/trigs/ electrolytes etc are?