Heroin overdoses are most commonly caused by respiratory failure. This results from high doses of most opioids, because they slow your breathing as well as your heart rate. The dose at which this occurs with heroin is approx. 400mg for a non-tolerant user.
Mixing heroin with other drugs or alcohol may increase the risk of overdose.

http://www.thegooddrugsguide.com/heroin/overdose.htm
http://www.peele.net/lib/heroinoverdose.html
http://bmj.bmjjournals.com/cgi/conte...316/7128/327/i
Nullific Reviewed by Nullific on . Heroin OD. So, I've gotten a lot of shit about this, but, heres the story: My boyfriend passed away last month of what was said to be a "heroin OD", and I've had a lot of people say that the shit can't kill ya. (Well, ya fuckers coulda prooved me wrong). I've heard that snorting H gives ya a pretty big risk, and that's what he'd done. Further investigations are leading up rumors that the shit was laced, but I stick with blunts and bowls so I'm not real big on the harder drugs, so sorry if this is Rating: 5