http://en.wikipedia.org/wiki/PoppersCitat:
Inhaling nitrites relaxes smooth muscles throughout the body, including the sphincter muscles of the anus and the vagina.[5] This causes the blood vessels to dilate (which causes a sudden drop in blood pressure), increases heart rate, and produces a sensation of heat and excitement that usually lasts for a couple of minutes.[8]
Alkyl nitrites are often used as a club drug or to enhance a sexual experience.[6] The head rush, euphoria, uncontrollable laughter or giggling, and other sensations that result from the blood pressure drop are often felt to increase sexual arousal and desire.[6] At the same time, the relaxation of the sphincters of the anus and vagina can make penetration easier. [9] It is widely reported that poppers can enhance and prolong orgasms.[1]
While anecdotal evidence reveals that both men and women can find the experience of using poppers pleasurable, this experience is not universal.[10] Some men report that poppers can cause erectile problems.[1]