I played around with Roy Bensons book "Precision Running with a HRM" while we were in the US. His training method is quite simple -- just running to different heart rate numbers, no pacing involved.
He encourages people to do lots of easy running to a maximum of 75-80% of your max HR and also encourages people to do fartleks by running until HR gets to around 90% and then recover back down to 70%.
I tried this out while we were away and found the method to be quite good -- except that the Fartleks never ever felt right to me . So -today I tried something different which I think will work for me . Easy slow running is boring!! -- but it has to be done -- lots of it!! And a big problem for me is that as soon as I hit any kind of hill, I must slow down even further, maybe to a walk , to keep my HR down. So today, I turned that around 180 degrees. I ran easy down all hills and on the flats - but whenever I came across any hill, regardless of length or steepness, I would run as hard as I could until my HRM registered 90% or I simply ran out of steam- then I would walk until I recovered . Sometimes I would try to get to the top of the hill and therefore restricted my effort to make sure the HR reached 90% at the top - while other times I would run as hard as possible, knowing that would I not reach the top, recovered and did it all over again until I did reach the top.
It kind of gave me some structure to adhere to for the Fartleks, made the slow run less boring - while at the same time relieved the SLOOOW slog up the hills that I would have had to do to keep in the aerobic zone .
I think this is going to work for me!!