What is a good carpet cleaning solution for heavily stained carpet?

Folex which is available in The Home Depot is wonderful for spot cleaning.

If you are looking for a solution to go into a machine, Capture. You can buy it at most home improvement stores.

Answer

If your carpet is extremely dirty, it may be beyond cleaning. Your best bet is to hire a carpet cleaner with a truck-mounted system who pre-spots the carpet. Still, it may not come out entirely (just depends on the type of stains and how matted the carpet is).