If your pet's matted hair is confirmation of a difficult life before you rescued him/her or the fact that he/she just plain likes to play hard, you will want to remove the knots and tangles as quickly as physically possible. You will not only relieve your pet from discomfort, you will have the pleasure of running your fingers through your pet's fur once again. There are professional dog groomers who specialize in de-matting dog fur, with the right equipment and know-how, you can save yourself $$$ and untangle any pet's matted fur right in your own house.
The first step is to run your fingers in the pet's fur to locate all knots, both concealed and on the surface. Attach a clothes pin to these tangles to separate them from the rest of the hair. Give special attention to the undercoat, the fur that is near the skin.
Now, rub each tangle thoroughly with a detangling product. The product can be bought at a pet store but you can use your own if you want. If you do not have any, use conditioner mixed with vegetable oil, mixed with cornstarch. You can also buy a specially formulated gel or spray from any local pet store.
Next, separate large tangles of fur into small parts, either with your fingers and/or a thin object such as an icing spreader or cheese knife, or with a "mat splitter". "Mat splitters" are special professional grooming tools (you can buy one at most pet stores) with blades that aid in the separation of your pet's tangle while keeping the length of the hair.
Finally, detangle bigger less thick knots with your fingers. Simply locate each knot inside the tangle and gently separate it until you can observe how the knot is made. Gently loosen the tangle and untie it with your fingers. This step is the most laborious and tiresome step, so patience is very important at this step. If you do not follow this step, when you go to comb the pet's hair, you will end up getting frustrated at your comb will probably break.
You can now brush or comb through each mat with gentle strokes on the top. Don't brush or comb too deep at first, just skim the top surface. Manually hold the tangle close to the undercoat while you are brushing so that you can keep the slicker brush from irritating the skin and causing your pet discomfort.
Scratch the lasting tangles with a wide-tooth comb. Keep your strokes vigorous and light-handed. Your pet will soon thank you for relieving it of its matted fur!