The document discusses how erections occur through the nitric oxide pathway and the effects of ginseng and Viagra. Ginseng increases nitric oxide to activate guanylyl cyclase and cGMP, relaxing smooth muscles. Viagra inhibits phosphodiesterase from breaking down cGMP, also relaxing muscles. If neither work, a problem with PKG, which activates through cGMP to decrease calcium and relax muscles, could be the cause.