Why spend time on pumping if you can do cardio?
Een couple of miles running makes the blood come everywhere, and improves your cardio-vasculair system a lot more than a set of infinity reps.
Pumping doesn't make the muscle grow, believe.
Check out the different types of musclefibers.
Type I
Type II (or IIA)
Type X (or IIB)
Nothing fancy, strictly science. Pumping (as in endless reps) activates type I, and that's a muscle with absolutely no growth-potential,
better to use a cardio session that makes active use of the muscle like swimming or crosstrainer.