Speedballing is a drug term for the mixing of heroin and cocaine. This is a potentially lethal concoction: the cocaine acts as a stimulant, raising the heartbeat, but its effects wear off more quickly than those of heroin, which in turn slows the heart. As a result, it is possible to experience a delayed "overdose" (technically, severe respiratory depression) when the stimulant wears off and the full effects of the heroin are felt in isolation.