Having an injury to one part of your body will not limit your ability to exercise another part of your body. So if you have a shoulder injury, you'll still be able to do your cardio. That being said, be aware of your injury and don't do anything that could make it worse.

Don't cheat yourself by making lame excuses. Just because your finger hurts doesn't mean you shouldn't do your workout. On the other hand, you need to be honest about how your injury really affects you. If you have a serious injury, it's ok to cut back on the frequency and duration of your workouts or stop altogether if your doctor tells you to.

Using common sense also applies to injury prevention. Be aware of your surroundings and know your limitations. Don't try to show off to impress someone.

If you have a lower-extremity injury (hip, knee or ankle), you can still do low-impact cardio like swimming, rowing, arm ergometry or shadowboxing. Focus your resistance training on your upper body with exercises for your back, chest, abs and arms.

If you have an upper-extremity injury (shoulder, elbow, wrist), you should be able to do most of your usual cardio (running, walking, biking, stair climbing) with the possible exception of the elliptical (or at least the arm portion). Additionally, exercises like lunges, squats, leg presses and dead lifts should be manageable.

If you have a back or neck injury, you need to be especially careful with the type of exercises you perform. Talk to your doctor about specific exercises you should be doing. Generally, swimming and recumbent biking are good ways to get your heart rate up without aggravating your exercise.c 

If the pain persists longer than three days, go to a doctor to have him/her evaluate your injury. Always follow all advice he/she gives you as far as how long to rest it and how to slowly reintroduce your injured limb to exercise. Avoid relying on the internet as your sole source of information. A doctor's advice always trumps a site like WebMD.c 

Injuries happen, but they don't have to mean the end of your fitness routine. It's ok to have to take a few days off to recover, but make sure you get back into your workout schedule once you're feeling better.

To avoid injuries in the first place, make sure you always do a proper warm up and cool down. Warm up with 5-10 minutes of light cardio or body-weight exercises and cool down with 5-10 minutes of stretching. Check out more about warm ups and cool downs here.