If you're serious I think you should pick up the book "the cyclist training bible" by joe friel. It has a good section about training by heart rate and determining your 'training zones' based off your LTHR. And it really is a great source of information about periodization and planning for several months of training ahead of time.
Hope this helps some, I highly recommend you pick that book up it is a GREAT place to start but there are several out there, read em' all
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