Sooooo.... You're HR does not elevate when you do weights?
Doing cardio to "keep fat off" while "trying to get as big as possible" is kind of like hitting yourself in the head with a hammer because it feels so good when you stop.
Is cardio important? Yes.. But "no cardio= un-healthy" is for sedentary folks.. IMO weight training is sufficient cardio as far as health reasons go. You may never run a four minute mile if you rely on weights as your sole means of exercise, but then again, we all have different goals.
You should NOT do cardio on a mass cycle to "keep fat off." THis is really funny to me.. Guys will do cardio and then eat 5000 cals/day... If you are concerned with getting fat on a cycle, don't eat so damn much.
Andy