In part 1 of Cardio can Hurt Fat Burning and Weight Loss, I discussed the misunderstanding of "cardio" and what it actually is and the benefits of cardiovascular exercise. Now I'll go into the negative effects of too much cardio on your long term fat burning and weight loss goals and how you can fix it.
First of all let me go back to what most people consider "cardio" exercise. Most people consider cardio as running, stair stepping, spending time on an elliptical and or similar machines. This is usually done at a low intensity (with respect to one rep max) for an extended period of time. This does a great job of burning calories, but unfortunately not from a specific source. Meaning that too much cardio can actually burn muscle. Burning off muscle will have the effect of lowering your metabolism. Not a good thing if you are trying to burn fat, go for the toned look, or keep your weight down long term.
So what's the fix? Partially it's understanding that cardio can be any activity that keeps your heart rate elevated for an extended period (generally 20 minutes or more), including weight training. So instead of doing what most consider a cardio workout, use a method (weight training) that will stimulate your lean body tissue and boost your metabolism instead of spending a lot of time on exercise that can actually tear down your lean body tissue and slow your metabolism.
The key to using weight training as cardio is to keep rest periods between sets or circuits low enough to keep your heart rate elevated. But there's another issue you also have to be aware of that makes this a little more complicated. The rest period required for a specific muscle or muscle group between sets has to be long enough so that the weight you can use is heavy enough to stimulate that muscle sufficiently. These issues are what makes putting together a complete workout program difficult. Fortunately, if you want to try this out for yourself, you can check out the Fat X Program (FX12). Here's workout 12 of the FX12 so you can see a sample of how you can keep your heart rate elevated and get your cardio workout in while weight training.
You can try the program as is and I'm sure you will get great results, or use the method and outline to develop a program for yourself.