You should make your work-outs high-intensity in terms of cardio. It's called interval training.

Basically, when you run, bike, whatever, you sprint for approximately 20 seconds, then slow down to a steady pace for 40 seconds. You repeat this over, and over.

You can apply this to any exercise you do, push-ups, etc. Same thing. Do 20 fast push-ups, rest for xxx of time, and do it again. Over time, you can adjust the intensity, by adding more time to the sprints/exercise.