I had the same problem in August (no cat in house) A/C broken, as a result the smell worsened and it was obvious something had died in the wall. Due to the extreme heat the decomposition process was accelerated and the smell was gone in a few days. I am now having the same problem in 2 different locations and outside temp is in the 30s so I have the heat on. The smell is really making me nauseous but even if I crank the heat I don't think it will work because the space behind the walls to exterior is uninsulated (freestanding rental apt. smell is in attic bedroom) Any suggestions?? I can't access the space of death and the cold weather has probably slowed the decaying...UGH!