Its best to ignore your heart in these situations. Attempting to feel its state or speed is asking for a decent into paranoia and fear. I find it best to just rely on the good chap to do his damn job like man and hopefully laos realize that nobody said it would be an easy job in the first place.
Anyways, if he lets you down he is done for as well, so that's a pretty good damn incentive for him to keep on going no matter what, if you ask me. So far this has worked out well.