Cardio when done right can only benefit your training and physique. However, most average meat heads in the gym do cardio the wrong way. They think that more is always better so therefore when they do there cardiovascular training they always overdue it.
The proper way to do cardio as a bodybuilder would be to do it the high intensity way, instead of the marathon way. When you do cardio do it before weight training or on days when your not weight training, due to the fact that cardio after training can seriously negatively effect the bodies recovery ability and totally screw up your strength and muscle gains.
The way I do my cardiovascular training is usually before I start weight training, I step on the treadmill walk for five minutes then put the machine on full speed and sprint for five minutes. This is how you effectively burn lots of calories while not putting your body in a catabolic state.
Therefore to break it all down in a very easy format to understand to do proper cardiovascular training the bodybuilding way you should:
1. Before weight training step on the treadmill or a exercise machine of your choice
2. Do a five minute warmup by keeping the pace nice and easy. After you feel warmed up begin to make your speed faster and faster, hold the highest speed you can take for five minutes of sprinting
3. Do some light strecthing and begin your weight trianing session