Jimi Hendrix neither had alcohol or heroin when he died.

He aspirated his own vomit and died of asphyxia while intoxicated with barbiturates. Specifically, large doses of the sleeping pill Vesparax.

Opioids kill by slowing breathing, full stop. The medical term is "Opioid-induced Respiratory Depression." Narcan very rapidly reverses this, which is how it saves lives.