Heart Rate Training

For those short of time (I know I am terribly long winded): two questions: 1. anyone here use heartrate as a major training aid or guide? 2. how do you monitor it if you do. 2a. if you use an electronic monitor, which one do you like? The reason I ask this is because I am attempting to go scientific on my training. Since I have started with "race pace" training, where nearly 25 to 30 % of my training time is dedicated to swimming fast, I have become progressively more interested/ concerned about how hard I am actually pushing myself. The crux of the matter came one day when I actually had to back off due to an impending loss of consciousness (at least I assume that is what it was: black spots in front of my eyes and an overall foggy thought pattern that centered on "STOP" and not much else). I have looked into heart monitors. I actually have one of the wrist-watch-only modules. It works poorly and unpredictably (and not at all right now with a presumably dead battery). My problem is that I have an abnormally slow heart rate at the best of times (bradycardia is what my insurance company likes to call it: 36 to 40 sitting still and I have no idea what it might be first thing in the morning). My blood preassure is borderline rediculously low most of the time (another issue with my insurance company). On the other hand, when I exercise my pulse can easily go to 200 or more, which is not likely to be too healthy at my 48 years of age. I don't worry too much about that; it drops practically instantaneously once I stop moving. Unfortunately that drop occurs so quickly that my wrist watch monitor never actually catches the real post repetition pulse; it takes 20 seconds to equilibrate and by that time my pulse is back down to 100 to 120. The other issue is that when I am really busting my gut I have trouble focussing my eyes so the reading on the pulsimeter is just a blur. I have used the old fashioned fingers and pace clock system, but when I am fighting for every breath, counting pulses is often more than I can manage. BTW: my huge variance in heart rates is more of a symptom of how inefficent a swimmer I really am rather than my fitness level. I would really like to get a top quality pulsimeter and see if I could use it for training. Any comments on how those units with the chest strap work? Is the chest strap hopelessly irritating, especially if you are really giving it your maximum effort? If I could get a really good pulsimeter at a reasonable price (cheap enough that my wife would not need a complimentary piece of jewelry to keep her happy) my coach has all sorts of drills based on heart rate and rest times I would love to try for a while. Or I could just manage not to blow a valve out of my heart by training more intelligently.