A broken toe severely limits your options for cardio exercise. You shouldn't do anything that jars your injury or stresses the area, so running, jogging, dancing, aerobic classes and other high-impact cardio workouts are off your schedule until your toe heals. However, there are plenty of exercises that elevate your heart rate and burn calories without putting pressure on your foot. Listen to your body, and don't return to high-impact cardio until your toe is pain-free and your doctor clears you to use it again.
Swim or take a water aerobics class. The buoyancy of the water allows you to keep all your weight off your toe. To increase the intensity of your cardio workout, swim with a T-shirt on.
Cycle, either on the streets or in the gym. If you use a stationary bike, try upright and recumbent varieties to see which one is more comfortable for your toe. Press the pedals with the ball of your foot, keeping the pressure off your injury.
Use a rowing machine at the gym. Rowing machines provide a cardio workout that uses primarily the upper body, so the risk to your toe is minimal.
Experiment with elliptical machines as you recover. Ellipticals are lower-impact than treadmills, so you might be comfortable using them before you are able to jog or run. Don't use the elliptical if it hurts your toe.
Continue doing cardio exercise for at least 30 minutes each day, five days each week while you are injured. Vary your workouts every few days to keep yourself interested and to consistently push your body. Increase the duration or intensity of your workouts as you gain strength and stamina. When your injury has healed fully, return to your previous cardio routines gradually.