Think cardiovascular excersises! The treadmill, biking...stuff that gets your heart-rate up. I would recommend doing it in speed intervals, as in starting a low speed for a set amount of minutes, then at a faster speed for the same amount of minutes as the slow speed, and then back to the slow speed...do this for a total of 30 minutes. This works because it helps your burn calories and fat more efficently - and you are also training your heart to become stronger. It becomes stronger because you start slow, then move fast, then go back to slow, and go back to fast, etc.