Heartbeat
You stand in the middle of Emergency Operations.
The room is huge but silent. All the activity has ceased,
or is there something wrong with you. There are several tables
full of equipment and few monitors showing something.
This is the place where we try to revive people who have lost
their heartbeat, if you think there is something wrong with you
just ask for help ('ask help', 'help me')
Not being a coder myself, I don't have a reliable understanding of heartbeats or how the game uses them, but I can make some educated guesses, and even a fuzzy idea can help a player have a better (mis)understanding of how the game works. In other words, what follows is about 65% guesswork, but hey, at least you can pretend to be all wise and knowing in front of your friends if you quote all my cool theories.
A heartbeat can be thought of as the smallest meaningful increment of time for many objects in Batmud, most especially players and monsters. One heartbeat is equal to three seconds, and except for some prescripted events such as those involving player movement, most nonplayer objects in the game tend to be completely frozen between them. For example, if you run into a room with an aggressive monster, 99.9999% of the time you'll have till the next heartbeat for it to notice you. This is why sometimes upon stumbling into a huge aggro, you can fumble and typo for what feels like quite a long time and still manage to get out before it starts attacking you. Other times, the aggro notices you in a fraction of a second and starts reaming you. The difference between these instances was where you fell on that three second scale each time you entered that room.
Where this gets more interesting is that there are races, abilities, and equipment that can cause heartbeat related timers to work differently. Perhaps the simplest example of this is your regen tick. (You know, the periodic regaining of hp, sp, and ep that happen while you're surfing goat hentai in another window.) Normally, characters have a thirty second, ten heartbeat tick. The most common way to see this altered is with fast heartbeat races, such as duck. These races get a chance each heartbeat for it to count twice or so. Thus, fast heartbeat races will often tick in 27 or fewer seconds. The fast metabolism boon helps in the same fashion, and stacks with fast heartbeat. This advantage works better with high tick numbers from hpr/spr eq, but will always help those blessed with it recover faster.
Another advantage of fast heartbeat is that skills and spells work on the exact same kind of heartbeat timer, and benefit in the same way as regen ticks. Each # of a spell can be thought of as a three second wait, and for those rare characters who can see their skill timers, it is the same.
Of course, there are ways to lose heartbeats as well. The weak heart bane and ents at wintertime can suffer from greater than thirty second ticks, and will see their spells and skills gong off slower too. So be careful what kinds of disadvantages you accept upon yourself!