His wife killed him, he ate undercooked pork, a fever or of course a jealous Salieri are some of the theories I heard. I know that we may never be 100% sure on this- but what was the most likely cause of death?
The theory I’ve heard most often is the undercooked pork one.
It’s likely that you’ve done a quick google on this and perhaps come up with the page that I’ve linked below, if you haven’t though, it makes an interesting read. 
I believe the most accepted theory to date is a sudden attack of scarlet fever. There’s an article about it on one of my professors doors at my school, but I haven’t bothered to read it in a few years, so I’m going by a very weak memory at the moment.
I believe that all of his symptoms were consistent with scarlet fever. Furthermore, he had been ill with it earlier in his life.
G’day
Carl Bär is supposed to have shown that Mozart as a result of being bled by his doctors during a bout of rheumatic fever, because of heart damage caused by previous bouts of rheumatic fever.
Regards,
Agback
One thing to keep in mind is that we can never really know for sure, because the way he was buried (see this page) means we cannot find his remains and run tests for any of these theories. So things have to remain likely but unproven.
yeah, I think I meant rheumatic fever.
Everybody KNOWS that Mozart was poisoned by his rival.Antonio Salieri!
Salieri WAS the better composer!
Because of the somewhat false ideas that came from the movie Amadeus, many people believed that it was in fact Salieri who poisoned or otherwise murdered Mozart, though this is not true. Historians have never come to a true conclusion to how he died, though there are many ideas that came up. Just about 75% of composers probably died from an STD, such as syphillus, so why not Mozart? Others say it was a heart or liver problem because he drank to much. Heck, it could have been a severe case of influenza.
The real answer: there is none, nobody really knows
My opinion: He died due to drinking too much, too often.
Wasn’t me–I was never even in aisle five!!