Running increases you vo2 max and gives you a good "base" for your cardio. But, for real cardio conditioning you have to train more sport specific.
I learned this the hard way. I ran my ass off for months before I stepped into a gym to train. Felt like a waste of time, I gassed so fast it was funny (to everyone else).
In my opinion swimming helps more than running.
I've never thrown up so often from overexersion then when I was on the swim team. That's taxing for sure.