After WWII, less and less Eastern Europeans, Russians and otherwise, feared Stalin. Some of the more left wing Russian citizens claimed that communism was running them into the ground, forcing Russia to become a third-world country, but a superpower nonetheless. They started to open their eyes to the fact that Stalin and other first-class Russians had a great deal of money compared to their lower class counterparts. So, since Stalin was becoming less revered as time went on, it was certainly a possibility that he was assasinated. However, it is very improbable because of the ramifications of assasinating that kind of leader. It would be much more likely that his death was induced, or, that it was an accident and simply, no one cared. If, as some suggest, that he died from a cerebral hemorrhage, then that would explain the"gurgling" noise that Belia described, but usually hemorrhage victims do not urinate. Yes, the soldiers were ordered to not enter his room, but it was more probable this order was given so as not to disturb him. So, there IS a possibility he was assasinated, but there would've been a very small window for the assasination to take place, and if the assasin simply snuck a poison into the food, then his food was obviously not being examined, thus helping the theory of Russia disliking Stalin towards the end of the 1940's and early 50's.

Source: http://stalin.narod.ru/ I also have a book on the subject, but i cannot recall the name, i will most certainly look.

Edit: more writing and a source.