In college i wass taught that endurance cardio ia wrong, that human beings are an animal, fundamentally, and if you look at other animals in the animal kingdom, no other does endurance running, or running "for fun".
Sprints on the other hand are prevalent, for hunting, running away, etc, so if there is any cardio to be done it should be in short bursts of high intensity.
It makes sense to me that endurance overwork their heart by putting constant strain on it, marathon runners and other high performance long distance athletes tend to have a lot of heart conplications later in life, and many of them never touched a steroid.
I only recently started doing it(cardio) and i do a moderate ammount at a moderate pace, but i think that after everything i have read, doing it on a bulk while on gear is asking for trouble.