Doing interval training has changed me as a rider....for the better. I've been working with a coach for about a year now, and HR Intervals are one of the main tenants of the program. There are many different kinds - most common being hill climbing intervals. Get on Blackstar - warm up for 20min., hammer for 3 min, bringing your HR up between 170-180 (depending on your max HR rate or lactic threshold), then cool down for 1:30, repeat. I usually do about 6 or 7 of those before I get to Beek's Place.
You need to figure out what your lactic threshold is first, so that you can properly set your zones. Send me a private message if you're interested and I can explain more.
Over time, your ability to endure long, hard efforts will become easier - and especially your ability to recover quickly.
Blackstar, Maple Springs, Harding are all great HR interval routes.