I would suggest soccer, I believe out of any sport you do the most constant running here (unless you're the goalie), and it is a fairly long game. I would also suggest basketball, swimming, or biking.
I think every sport is health beneficial specifically in your cardiovascular system. But since you want a specific sport here's a good one: running or biking.
It has been proven that cross-country skiing demands more of the cardio vascular system than any other sport. This is because competitive events usually take place over very long distances and skiers encounter lots of different inclines to conquer.
fighting, muay thai, boxing etc. plus its fun to hurt ppl. hockey if u live in canada, and id also agree with the soccer. but anything u enjoy is best. the more u like it the more u will actually do it.
You can also do what is called the S.M.I.T (Supramaxmial Interval Training.) It involves performing maximal intensity (all out) burst of exercise interspersed with rest periods (no activity). The more intense the work interval the longer your recovery time.
This can help you with your cardio if you don't have much time.