In Case of Emergency, Do Not Call an Olsen Twin

Twice. Now I don't know the Olsen twins personally, but I can't think of anyone more ill equipped to provide appropriate advice in a dire situation, other than perhaps (perhaps) an infant. If you think you should call 9-1-1, for God's sake call 9-1-1.

It's currently unknown what killed Heath Ledger, and it's unknowable if an earlier call to 9-1-1 would have saved the actor; however, news reports indicate the presence of several prescription drugs in his apartment, including the benzodiazepines diazepam (Valium) and alprazolam (Xanax), as well as the non-benzodiazepine sleep aid zolpidem tartrate (Ambien). I have also seen stories indicating the presence of a prescription antihistamine in the apartment.

It's difficult to kill yourself with an overdose of a benzodiazepine alone, because of the generally wide therapeutic window associated with the medication class—meaning that the dosage that causes sedation is much lower than the dosage that causes respiratory depression. Given the current information, it appears most likely that Ledger succumbed to the effect of 2 or more, possibly overdosed drugs—specifically a benzodiazepine and Ambien (and possibly an antihistamine, depending on the agent). The prescribing information for Ambien contains the following text:

In postmarketing experience of overdose with zolpidem tartrate alone, or in combination with CNS [central nervous system]-depressant agents, impairment of consciousness ranging from somnolence to coma, cardiovascular and/or respiratory compromise, and fatal outcomes have been reported.