im not really sure what you mean with "dying heart" but here are some pointers
-- slow heart rate
tachycardia -- fast heart rate (also regualr)
-- very tough to explain, usually a normal heart rhytm has one small spike, followed by one big spike, then another small spike. with ventricular fibrillation -- it's completely abnorma and out of sync -- it's all small spikes and no pause in betwen.
-- is all big spikes with no rest in between.
Asystole -- is no rhythm at all
i think when you say "dying heart" you meant heart attack
-- you see, what happens with heart attack is that you get chest pain -- because blood is not able to travel to a specific muscle in our heart (because of some blockage) -- that muscle is trying to work, even if no oxygen is supplied to it -- that's what causes the chest pain. when suddenly, the pain goes away -- it could mean 2 things:
good -- that the blockage has been dislodged
bad -- the heart muscle died -- and that's probably what you meant with "dying heart"