Aye. If I go on a long, slow run (say 10 miles +) to build up my base i'll try and run at a tempo that keeps my heart rate at roughly 135 - 145 bpm.I'll maybe then later in the week try a shorter but much faster run where my heart rate is nearer it's maximum (roughly 185 bpm).
I think, in short, it's a good idea to keep an eye on your heart rate throughout your run just so you're not putting too much stress on your heart every time you head out. Also, if you're constantly training near your max bpm you'll be at a level where your body finds it really difficult to remove all the excess lactic acid.
Edit - might be talking pish with the last bit but i'm sure i've heard that before. Somebody else on here will know better than me.