I know eric agrees, but I disagree with this. If you just try to pack on random amounts of poundages because they are "heavy" then you may wind up injuring yourself or doing workouts improperly (which goes hand in hand)

If you wanna take ur intensity to the next level I suggest a training Journal. If you keep track of what you are doing each time, and notice you havent increased in a while, bump up the weight a little......that means the block you have hit is probably more mental.

When i feel I am having a hard time lifting the heavy weights and want to pump up my intensity and still get a nice big pump out of my muscles, I superset.

According to Arnold's Bible of Bodybuilding, after 3 minutes rest, your muscles are 92% recovered. After 1 minute, they are approximately 50% recovered. Rest no longer than a minute, because according to the New Encyclopedia of Modern Bodybuilding you want to keep your muscles in a recovery/unrecovered state while you are doing your workouts to recruit more fibers that will encourage muscle growth.

In short, make sure to rest but definitely keep your rests under a minute and if you are having a hard time getting that pump, try supersetting with 0-30 sec rest at most. That's whats helped me.