Help! My heater smells like pee!

The heater in my 90 Geo Storm smells like urine the warmer it gets. When I first got the car a few months ago it was VERY strong and since running it, it has very gradually lightened up a little, but is still strong enough that I really need to find out what is causing this so I can get it fixed. Nobody will ride with me because it stinks! It's only when the heater is on, and the hotter it gets, the stronger the urine smell. Any help you could give me would be greatly appreciated.:feedback:

well! had this modified Suzuki samurai, somebody squirted a little/ lot of elk urine cover scent down the defroster ducts, stunk for almost a year! sounds like this may be the case, although it may be some other form or urine, unless it was done on purpose, I'm guessing cat urine, you got a couple of options, either dump baking soda down the defroster ducts ( make sure that's where the smell is worst) or you can also use coffee ground (couple of table spoons dry ), these 2 will absorb the smell, when the smell is gone, tape a small rubber hose to your vacuum cleaner hose, and snake it down the duct to vacuum out the baking soda/ coffee.
for the record! mine was done as a prank, and we towed the Samurai to eastern Oregon with the top off!
hth
Rick, Ore