Dogs with long or thick coats are prone to developing tangles, which then develop into mats. Mats are not only unattractive, they can be painful for your dog. The tangle can be so tight that it pulls on the skin. Removing mats is a also a challenge. If your dog's coat is severely matted, plan to break the job up into several days. This will make it more tolerable for both you and your pup.
Spray your dog with detangling spray. This will soften and smooth the hair, making the mat a little easier to slide loose.
Work on one mat at a time. Don't try to run a comb through the dog's coat at this point, simply pick one mat and start picking it loose.
Pick at the mat with your fingers, working from either side. Starting at the bottom of the mat and working up can inadvertently tighten the mat.
Use the edge of your metal comb to loosen the mat after you have picked as much of it loose as you can. Slip two or three of the comb's teeth into the mat and work the knot loose a tiny piece at a time.
Insert a mat splitter into the center of any remaining mat and pull towards either side of the mat. Make several passes with the splitter, moving from the center of the mat to the edge each time. Never pull toward your dog's skin with the splitter, which has a cutting blade in it. After several passes, you should be able to pick the remaining mat out of the coat.
Run the metal comb through the previously matted area, to make sure the entire tangle is gone.
Move to the next mat to repeat the process. Remember to break this job up into several short sessions to make it easier for you and your pup.