I'm confused about the link between heart rate and metabolism.

Scenrio for an example: when someone drinks a few cups of coffee they consume all the caffeine, which hits the blood stream and triggers heart to release adrenaline -- in turn increase heart rate. As the heart beats faster all bodily process speed up simultaneously. Breathing becomes heavier, thought patterns become more erratic, sight in some people becomes more focussed, increased blood flow increases flexibility, etc. Because of the increased rate at which the body is now running itself as the machine that it is its energy is burned at a faster rate.

In short, caffeine increases heart rate which ends up temporarily increasing metabolism.

Now, when people are really cold and their heart rate slows down their metabolism also slows down, correct? The heart isn't working as hard; it's pumping less blood to the muscles and organs, and thus requires less fuel for its job.

So, how is it that healthy individuals, especially exceptional ones like elite athletes, who have particularly low resting heart rates have significantly faster metabolisms than the general public?