Interval/Burst Training:
Research is showing the BEST way to condition your heart and burn fat is with burst training.  It takes less time than a typical cardio work out and it has better results.
The activity typically requires 30 sec of high-intensity exercise with 90 sec of gentle recovery such as moderate jumping jacks or a slow jog.
One study showed you could burn more fat exercising for 20 minutes than for 40 minutes!
Try this one out!