My normal heart beat is 72, when i do aerobic exercise i get it up to 130 but twice during the exercise and aftere approximately 25 minutes it had suddenly dropped from the 130 to about 75, quite regular though at 75, it happened once whilst bending and once doing crunches.
Pacemaker is set at 60 so thats not in play. Both times i have stopped the
exercise and gone into cool down mode.