What are some exercises I can do to increase my cardiovascular fitness?

Well, swimming would help, for one thing. At my team, we do breathing excercises, also. Like holding your breath for a certain ammount of time, then slowly releasing. That helps. We do yoga on mondays and fridays in order to concentrate on breathing. We run three days a week, which helps with all around fitness, also. About once a week, we run in the water, which ends up being extremely hard if you’re doing it for twenty minutes or so.

I vote just work on your breathing. Yoga is extremely good for that, but if you just want something to do at home, take in a deep breath, concentrating on filling your lungs from bottom to top (your stomach should come out, your shoulders should not come up too much). When you think you’ve taken in the maximum ammount of air, hold for a few seconds, then take in more. Then hold your breath until you start to feel dizzy/think you can’t anymore. Then slowly release. Jusst don’t kill yourself. We do this in the water too, which helps. But doing it a few times a day for a few weeks would help a lot, or like three times a week. Time yourself when you starts, and where you are a few sessions later. I saw a huge difference.