Amyl nitrite is (or was) used as an antidote for cyanide poisoning. Years ago in New Zealand you could buy over the counter, cards of small glass ampoules, as it was common to own a licence to cull possums by poisoning (then selling the skins). You'ld break these in a handkerchief under the nose and sniff. Hardly surprising, it was common to hear about mild cases of suspected poisonings.
This stuff was definitely different from the sustitutes sold in sex shops. The extra carbon in the chain makes all the difference, amyl being the pentyl form. In any form however, such inhalents are not on my personal preference list.
A point of warning if it hasn't already been been said. NEVER use Viagra with nitrite inhalants. Viagra inhibits the enzyme responsible for detoxifying and eliminating the effects of nitrites / nitrates. Serious trouble could result from this combination, probably from effects on the heart.
phase_dancer